The latest Android and Google Play news for app and game developers.
Posted by Janis Danisevskis, Information Security Engineer, Android Security
In Android Pie, we introduced Android Protected Confirmation, the first major mobile OS API that leverages a hardware protected user interface (Trusted UI) to perform critical transactions completely outside the main mobile operating system. This Trusted UI protects the choices you make from fraudulent apps or a compromised operating system. When an app invokes Protected Confirmation, control is passed to the Trusted UI, where transaction data is displayed and user confirmation of that data's correctness is obtained.
Once confirmed, your intention is cryptographically authenticated and unforgeable when conveyed to the relying party, for example, your bank. Protected Confirmation increases the bank's confidence that it acts on your behalf, providing a higher level of protection for the transaction.
Protected Confirmation also adds additional security relative to other forms of secondary authentication, such as a One Time Password or Transaction Authentication Number. These mechanisms can be frustrating for mobile users and also fail to protect against a compromised device that can corrupt transaction data or intercept one-time confirmation text messages.
Once the user approves a transaction, Protected Confirmation digitally signs the confirmation message. Because the signing key never leaves the Trusted UI's hardware sandbox, neither app malware nor a compromised operating system can fool the user into authorizing anything. Protected Confirmation signing keys are created using Android's standard AndroidKeyStore API. Before it can start using Android Protected Confirmation for end-to-end secure transactions, the app must enroll the public KeyStore key and its Keystore Attestation certificate with the remote relying party. The attestation certificate certifies that the key can only be used to sign Protected Confirmations.
There are many possible use cases for Android Protected Confirmation. At Google I/O 2018, the What's new in Android security session showcased partners planning to leverage Android Protected Confirmation in a variety of ways, including Royal Bank of Canada person to person money transfers; Duo Security, Nok Nok Labs, and ProxToMe for user authentication; and Insulet Corporation and Bigfoot Biomedical, for medical device control.
Insulet, a global leading manufacturer of tubeless patch insulin pumps, has demonstrated how they can modify their FDA cleared Omnipod DASH TM Insulin management system in a test environment to leverage Protected Confirmation to confirm the amount of insulin to be injected. This technology holds the promise for improved quality of life and reduced cost by enabling a person with diabetes to leverage their convenient, familiar, and secure smartphone for control rather than having to rely on a secondary, obtrusive, and expensive remote control device. (Note: The Omnipod DASH™ System is not cleared for use with Pixel 3 mobile device or Protected Confirmation).
This work is fulfilling an important need in the industry. Since smartphones do not fit the mold of an FDA approved medical device, we've been working with FDA as part of DTMoSt, an industry-wide consortium, to define a standard for phones to safely control medical devices, such as insulin pumps. A technology like Protected Confirmation plays an important role in gaining higher assurance of user intent and medical safety.
To integrate Protected Confirmation into your app, check out the Android Protected Confirmation training article. Android Protected Confirmation is an optional feature in Android Pie. Because it has low-level hardware dependencies, Protected Confirmation may not be supported by all devices running Android Pie. Google Pixel 3 and 3XL devices are the first to support Protected Confirmation, and we are working closely with other manufacturers to adopt this market-leading security innovation on more devices.
Posted by Nagendra Modadugu and Bill Richardson, Google Device Security Group
At the Made by Google event last week, we talked about the combination of AI + Software + Hardware to help organize your information. To better protect that information at a hardware level, our new Pixel 3 and Pixel 3 XL devices include a Titan M chip.We briefly introduced Titan M and some of its benefits on our Keyword Blog, and with this post we dive into some of its technical details.
Titan M is a second-generation, low-power security module designed and manufactured by Google, and is a part of the Titan family. As described in the Keyword Blog post, Titan M performs several security sensitive functions, including:
Including Titan M in Pixel 3 devices substantially reduces the attack surface. Because Titan M is a separate chip, the physical isolation mitigates against entire classes of hardware-level exploits such as Rowhammer, Spectre, and Meltdown. Titan M's processor, caches, memory, and persistent storage are not shared with the rest of the phone's system, so side channel attacks like these—which rely on subtle, unplanned interactions between internal circuits of a single component—are nearly impossible. In addition to its physical isolation, the Titan M chip contains many defenses to protect against external attacks.
But Titan M is not just a hardened security microcontroller, but rather a full-lifecycle approach to security with Pixel devices in mind. Titan M's security takes into consideration all the features visible to Android down to the lowest level physical and electrical circuit design and extends beyond each physical device to our supply chain and manufacturing processes. At the physical level, we incorporated essential features optimized for the mobile experience: low power usage, low-latency, hardware crypto acceleration, tamper detection, and secure, timely firmware updates. We improved and invested in the supply chain for Titan M by creating a custom provisioning process, which provides us with transparency and control starting from the earliest silicon stages.
Finally, in the interest of transparency, the Titan M firmware source code will be publicly available soon. While Google holds the root keys necessary to sign Titan M firmware, it will be possible to reproduce binary builds based on the public source for the purpose of binary transparency.
Titan (left) and Titan M (right)
Titan M's CPU is an ARM Cortex-M3 microprocessor specially hardened against side-channel attacks and augmented with defensive features to detect and respond to abnormal conditions. The Titan M CPU core also exposes several control registers, which can be used to taper access to chip configuration settings and peripherals. Once powered on, Titan M verifies the signature of its flash-based firmware using a public key built into the chip's silicon. If the signature is valid, the flash is locked so it can't be modified, and then the firmware begins executing.
Titan M also features several hardware accelerators: AES, SHA, and a programmable big number coprocessor for public key algorithms. These accelerators are flexible and can either be initialized with keys provided by firmware or with chip-specific and hardware-bound keys generated by the Key Manager module. Chip-specific keys are generated internally based on entropy derived from the True Random Number Generator (TRNG), and thus such keys are never externally available outside the chip over its entire lifetime.
While implementing Titan M firmware, we had to take many system constraints into consideration. For example, packing as many security features into Titan M's 64 Kbytes of RAM required all firmware to execute exclusively off the stack. And to reduce flash-wear, RAM contents can be preserved even during low-power mode when most hardware modules are turned off.
The diagram below provides a high-level view of the chip components described here.
At the heart of our implementation of Titan M are two broader trends: transparency and building a platform for future innovation.
Transparency around every step of the design process — from logic gates to boot code to the applications — gives us confidence in the defenses we're providing for our users. We know what's inside, how it got there, how it works, and who can make changes.
Custom hardware allows us to provide new features, capabilities, and performance not readily available in off-the-shelf components. These changes allow higher assurance use cases like two-factor authentication, medical device control, P2P payments, and others that we will help develop down the road.
As more of our lives are bound up in our phones, keeping those phones secure and trustworthy is increasingly important. Google takes that responsibility seriously. Titan M is just the latest step in our continuing efforts to improve the privacy and security of all our users.
Posted by Sami Tolvanen, Staff Software Engineer, Android Security
Android's security model is enforced by the Linux kernel, which makes it a tempting target for attackers. We have put a lot of effort into hardening the kernel in previous Android releases and in Android 9, we continued this work by focusing on compiler-based security mitigations against code reuse attacks.
Google's Pixel 3 will be the first Android device to ship with LLVM's forward-edge Control Flow Integrity (CFI) enforcement in the kernel, and we have made CFI support available in Android kernel versions 4.9 and 4.14. This post describes how kernel CFI works and provides solutions to the most common issues developers might run into when enabling the feature.
A common method of exploiting the kernel is using a bug to overwrite a function pointer stored in memory, such as a stored callback pointer or a return address that had been pushed to the stack. This allows an attacker to execute arbitrary parts of the kernel code to complete their exploit, even if they cannot inject executable code of their own. This method of gaining code execution is particularly popular with the kernel because of the huge number of function pointers it uses, and the existing memory protections that make code injection more challenging.
CFI attempts to mitigate these attacks by adding additional checks to confirm that the kernel's control flow stays within a precomputed graph. This doesn't prevent an attacker from changing a function pointer if a bug provides write access to one, but it significantly restricts the valid call targets, which makes exploiting such a bug more difficult in practice.
Figure 1. In an Android device kernel, LLVM's CFI limits 55% of indirect calls to at most 5 possible targets and 80% to at most 20 targets.
In order to determine all valid call targets for each indirect branch, the compiler needs to see all of the kernel code at once. Traditionally, compilers work on a single compilation unit (source file) at a time and leave merging the object files to the linker. LLVM's solution to CFI is to require the use of LTO, where the compiler produces LLVM-specific bitcode for all C compilation units, and an LTO-aware linker uses the LLVM back-end to combine the bitcode and compile it into native code.
Figure 2. A simplified overview of how LTO works in the kernel. All LLVM bitcode is combined, optimized, and generated into native code at link time.
Linux has used the GNU toolchain for assembling, compiling, and linking the kernel for decades. While we continue to use the GNU assembler for stand-alone assembly code, LTO requires us to switch to LLVM's integrated assembler for inline assembly, and either GNU gold or LLVM's own lld as the linker. Switching to a relatively untested toolchain on a huge software project will lead to compatibility issues, which we have addressed in our arm64 LTO patch sets for kernel versions 4.9 and 4.14.
In addition to making CFI possible, LTO also produces faster code due to global optimizations. However, additional optimizations often result in a larger binary size, which may be undesirable on devices with very limited resources. Disabling LTO-specific optimizations, such as global inlining and loop unrolling, can reduce binary size by sacrificing some of the performance gains. When using GNU gold, the aforementioned optimizations can be disabled with the following additions to LDFLAGS:
LDFLAGS += -plugin-opt=-inline-threshold=0 \ -plugin-opt=-unroll-threshold=0
Note that flags to disable individual optimizations are not part of the stable LLVM interface and may change in future compiler versions.
LLVM's CFI implementation adds a check before each indirect branch to confirm that the target address points to a valid function with a correct signature. This prevents an indirect branch from jumping to an arbitrary code location and even limits the functions that can be called. As C compilers do not enforce similar restrictions on indirect branches, there were several CFI violations due to function type declaration mismatches even in the core kernel that we have addressed in our CFI patch sets for kernels 4.9 and 4.14.
Kernel modules add another complication to CFI, as they are loaded at runtime and can be compiled independently from the rest of the kernel. In order to support loadable modules, we have implemented LLVM's cross-DSO CFI support in the kernel, including a CFI shadow that speeds up cross-module look-ups. When compiled with cross-DSO support, each kernel module contains information about valid local branch targets, and the kernel looks up information from the correct module based on the target address and the modules' memory layout.
Figure 3. An example of a cross-DSO CFI check injected into an arm64 kernel. Type information is passed in X0 and the target address to validate in X1.
CFI checks naturally add some overhead to indirect branches, but due to more aggressive optimizations, our tests show that the impact is minimal, and overall system performance even improved 1-2% in many cases.
CFI for arm64 requires clang version >= 5.0 and binutils >= 2.27. The kernel build system also assumes that the LLVMgold.so plug-in is available in LD_LIBRARY_PATH. Pre-built toolchain binaries for clang and binutils are available in AOSP, but upstream binaries can also be used.
The following kernel configuration options are needed to enable kernel CFI:
CONFIG_LTO_CLANG=y CONFIG_CFI_CLANG=y
Using CONFIG_CFI_PERMISSIVE=y may also prove helpful when debugging a CFI violation or during device bring-up. This option turns a violation into a warning instead of a kernel panic.
As mentioned in the previous section, the most common issue we ran into when enabling CFI on Pixel 3 were benign violations caused by function pointer type mismatches. When the kernel runs into such a violation, it prints out a runtime warning that contains the call stack at the time of the failure, and the call target that failed the CFI check. Changing the code to use a correct function pointer type fixes the issue. While we have fixed all known indirect branch type mismatches in the Android kernel, similar problems may be still found in device specific drivers, for example.
CFI failure (target: [<fffffff3e83d4d80>] my_target_function+0x0/0xd80): ------------[ cut here ]------------ kernel BUG at kernel/cfi.c:32! Internal error: Oops - BUG: 0 [#1] PREEMPT SMP … Call trace: … [<ffffff8752d00084>] handle_cfi_failure+0x20/0x28 [<ffffff8752d00268>] my_buggy_function+0x0/0x10 …
Figure 4. An example of a kernel panic caused by a CFI failure.
Another potential pitfall are address space conflicts, but this should be less common in driver code. LLVM's CFI checks only understand kernel virtual addresses and any code that runs at another exception level or makes an indirect call to a physical address will result in a CFI violation. These types of failures can be addressed by disabling CFI for a single function using the __nocfi attribute, or even disabling CFI for entire code files using the $(DISABLE_CFI) compiler flag in the Makefile.
static int __nocfi address_space_conflict() { void (*fn)(void); … /* branching to a physical address trips CFI w/o __nocfi */ fn = (void *)__pa_symbol(function_name); cpu_install_idmap(); fn(); cpu_uninstall_idmap(); … }
Figure 5. An example of fixing a CFI failure caused by an address space conflict.
Finally, like many hardening features, CFI can also be tripped by memory corruption errors that might otherwise result in random kernel crashes at a later time. These may be more difficult to debug, but memory debugging tools such as KASAN can help here.
We have implemented support for LLVM's CFI in Android kernels 4.9 and 4.14. Google's Pixel 3 will be the first Android device to ship with these protections, and we have made the feature available to all device vendors through the Android common kernel. If you are shipping a new arm64 device running Android 9, we strongly recommend enabling kernel CFI to help protect against kernel vulnerabilities.
LLVM's CFI protects indirect branches against attackers who manage to gain access to a function pointer stored in kernel memory. This makes a common method of exploiting the kernel more difficult. Our future work involves also protecting function return addresses from similar attacks using LLVM's Shadow Call Stack, which will be available in an upcoming compiler release.
Posted by Jason Woloz and Mayank Jain, Android Security & Privacy Team
Our Android and Play security reward programs help us work with top researchers from around the world to improve Android ecosystem security every day. Thank you to all the amazing researchers who submitted vulnerability reports.
In the ASR program's third year, we received over 470 qualifying vulnerability reports from researchers and the average pay per researcher jumped by 23%. To date, the ASR program has rewarded researchers with over $3M, paying out roughly $1M per year.
Here are some of the highlights from the Android Security Rewards program's third year:
As part of our ongoing commitment to security we regularly update our programs and policies based on ecosystem feedback. We also updated our severity guidelines for evaluating the impact of reported security vulnerabilities against the Android platform.
In October 2017, we rolled out the Google Play Security Reward Program to encourage security research into popular Android apps available on Google Play. So far, researchers have reported over 30 vulnerabilities through the program, earning a combined bounty amount of over $100K.
If undetected, these vulnerabilities could have potentially led to elevation of privilege, access to sensitive data and remote code execution on devices.
In addition to rewarding for vulnerabilities, we continue to work with the broad and diverse Android ecosystem to protect users from issues reported through our program. We collaborate with manufacturers to ensure that these issues are fixed on their devices through monthly security updates. Over 250 device models have a majority of their deployed devices running a security update from the last 90 days. This table shows the models with a majority of deployed devices running a security update from the last three months:
Thank you to everyone internally and externally who helped make Android safer and stronger in the past year. Together, we made a huge investment in security research that helps Android users everywhere. If you want to get involved to make next year even better, check out our detailed program rules. For tips on how to submit complete reports, see Bug Hunter University.
Posted by Dave Kleidermacher, VP, Head of Security - Android, Chrome OS, Play
At Google I/O 2018, in our What's New in Android Security session, we shared a brief update on the Android security updates program. With the official release of Android 9 Pie, we wanted to share a more comprehensive update on the state of security updates, including best practice guidance for manufacturers, how we're making Android easier to update, and how we're ensuring compliance to Android security update releases.
As we noted in our 2017 Android Security Year-in-Review, Android's anti-exploitation strength now leads the mobile industry and has made it exceedingly difficult and expensive to leverage operating system bugs into compromises. Nevertheless, an important defense-in-depth strategy is to ensure critical security updates are delivered in a timely manner. Monthly security updates are the recommended best practice for Android smartphones. We deliver monthly Android source code patches to smartphone manufacturers so they may incorporate those patches into firmware updates. We also deliver firmware updates over-the-air to Pixel devices on a reliable monthly cadence and offer the free use of Google's firmware over-the-air (FOTA) servers to manufacturers. Monthly security updates are also required for devices covered under the Android One program.
While monthly security updates are best, at minimum, Android manufacturers should deliver regular security updates in advance of coordinated disclosure of high severity vulnerabilities, published in our Android bulletins. Since the common vulnerability disclosure window is 90 days, updates on a 90-day frequency represents a minimum security hygiene requirement.
Product security factors into purchase decisions of enterprises, who often consider device security update cadence, flexibility of policy controls, and authentication features. Earlier this year, we introduced the Android Enterprise Recommended program to help businesses make these decisions. To be listed, Android devices must satisfy numerous requirements, including regular security updates: at least every 90 days, with monthly updates strongly recommended. In addition to businesses, consumers interested in understanding security update practices and commitment may also refer to the Enterprise Recommended list.
We've also been working to make Android easier to update, overall. A key pillar of that strategy is to improve modularity and clarity of interfaces, enabling operating system subsystems to be updated without adversely impacting others. Project Treble is one example of this strategy in action and has enabled devices to update to Android P more easily and efficiently than was possible in previous releases. The modularity strategy applies equally well for security updates, as a framework security update can be performed independently of device specific components.
Another part of the strategy involves the extraction of operating system services into user-mode applications that can be updated independently, and sometimes more rapidly, than the base operating system. For example, Google Play services, including secure networking components, and the Chrome browser can be updated individually, just like other Google Play apps.
Partner programs are a third key pillar of the updateability strategy. One example is the GMS Express program, in which Google is working closely with system-on-chip (SoC) suppliers to provide monthly pre-integrated and pre-tested Android security updates for SoC reference designs, reducing cost and time to market for delivering them to users.
Recently, researchers reported a handful of missing security bug fixes across some Android devices. Initial reports had several inaccuracies, which have since been corrected. We have been developing security update testing systems that are now making compliance failures less likely to occur. In particular, we recently delivered a new testing infrastructure that enables manufacturers to develop and deploy automated tests across lower levels of the firmware stack that were previously relegated to manual testing. In addition, the Android build approval process now includes scanning of device images for specific patterns, reducing the risk of omission.
In 2017, about a billion Android devices received security updates, representing approximately 30% growth over the preceding year. We continue to work hard devising thoughtful strategies to make Android easier to update by introducing improved processes and programs for the ecosystem. In addition, we are also working to drive increased and more expedient partner adoption of our security update and compliance requirements. As a result, over coming quarters, we expect the largest ever growth in the number of Android devices receiving regular security updates.
Bugs are inevitable in all complex software systems, but exploitability of those bugs is not. We're working hard to ensure that the incidence of potentially harmful exploitation of bugs continues to decline, such that the frequency for security updates will reduce, not increase, over time. While monthly security updates represents today's best practice, we see a future in which security updates becomes easier and rarer, while maintaining the same goal to protect all users across all devices.
Posted by Purnima Kochikar, Director, Google Play, Apps & Games
On Monday we released Android 9 Pie. As we continue to push the Android platform forward, we're always looking to provide new ways to distribute your apps efficiently, help people discover and engage with your work, and improve the overall security of our ecosystem. Google Play has had a busy year so far with some big milestones around helping you reach more users, including:
Google Play is dedicated to helping you build and grow quality app businesses, reach the more than 2 billion Android devices globally and provide your users with better experiences. Here are some of the important areas we're prioritizing this year:
We've added more testing tools to the popular Play Console to help developers de-risk app launches with internal and external test tracks and staged rollouts to get valuable early feedback. This year we've expanded the Start on Android program globally that provides developers new to Android additional guidance to optimize their apps before launch. Google Play Instant remains a huge bet to transform app discovery and improve conversions by letting users engage without the friction of installing. We're seeing great results from early adopters and are working on new places to surface instant experience, including ads, and making them easier to build throughout the year.
Google Play plays an important role helping developers understand and fix quality and performance issues. At I/O, we showcased how we expanded the battery, stability and rendering of Android vitals reporting to include app start time & permission denials, enabling developers to cut application not responding errors by up to 95%. We also expanded the functionality of automated device testing with the pre-launch report to enable games testing. Recently, we increased the importance of app quality in our search and discovery recommendations that has resulted in higher engagement and satisfaction with downloaded games.
Over the last year we've rolled out more editorial content and improved our machine learning to deliver personalized recommendations for apps and games that engage users. Since most game downloads come from browsing (as opposed to searching or deep linking into) the store, we've put particular focus on games discovery, with a new games home page, special sections for premium and new games, immersive video trailers and screenshots, and the ability to try games instantly. We've also introduced new programs to help drive app downloads through richer discovery. For example, since launching our app pre-registration program in 2016, we've seen nearly 250 million app pre-registrations. Going forward, we'll be expanding on these programs and others like LiveOps cards to help developers engage more deeply with their audience.
Google Play now collects payments in 150 markets via credit card, direct carrier billing (DCB), Paypal, and gift cards. Direct carrier billing is now enabled across 167 carriers in 64 markets. In 2018, we have focused on expanding our footprint in Africa and Latam with launches in Ghana, Kenya, Tanzania, Nigeria, Peru & Colombia. And users can now buy Google Play credit via gift cards or other means in more 800,000 retail locations around the world. This year, we also launched seller support in 18 new markets bringing the total markets with seller support to 98. Our subscription offering continues to improve with ML-powered fraud detection and even more control for subscribers and developers. Google Play's risk modeling automatically helps detect fraudulent transactions and purchase APIs help you better analyze your refund data to identify suspicious activity.
Google Play Protect and our other systems scan and analyze more than 50 billion apps a day to keep our ecosystem safe for users and developers. In fact, people who only download apps from Google Play are nine times less likely to download a potentially harmful app than those who download from other sources. We've made significant improvements in our ability to detect abuse—such as impersonation, inappropriate content, fraud, or malware—through new machine learning models and techniques. The result is that 99% of apps with abusive content are identified and rejected before anyone can install them. We're also continuing to run the Google Play Security Rewards Program through a collaboration with Hacker One to discover other vulnerabilities.
We are continually inspired by what developers build—check out #IMakeApps for incredible examples—and want every developer to have the tools needed to succeed. We can't wait to see what you do next!
Android's switch to LLVM/Clang as the default platform compiler in Android 7.0 opened up more possibilities for improving our defense-in-depth security posture. In the past couple of releases, we've rolled out additional compiler-based mitigations to make bugs harder to exploit and prevent certain types of bugs from becoming vulnerabilities. In Android P, we're expanding our existing compiler mitigations, which instrument runtime operations to fail safely when undefined behavior occurs. This post describes the new build system support for Control Flow Integrity and Integer Overflow Sanitization.
A key step in modern exploit chains is for an attacker to gain control of a program's control flow by corrupting function pointers or return addresses. This opens the door to code-reuse attacks where an attacker executes arbitrary portions of existing program code to achieve their goals, such as counterfeit-object-oriented and return-oriented programming. Control Flow Integrity (CFI) describes a set of mitigation technologies that confine a program's control flow to a call graph of valid targets determined at compile-time.
While we first supported LLVM's CFI implementation in select components in Android O, we're greatly expanding that support in P. This implementation focuses on preventing control flow manipulation via indirect branches, such as function pointers and virtual functions—the 'forward-edges' of a call graph. Valid branch targets are defined as function entry points for functions with the expected function signature, which drastically reduces the set of allowable destinations an attacker can call. Indirect branches are instrumented to detect runtime violations of the statically determined set of allowable targets. If a violation is detected because a branch points to an unexpected target, then the process safely aborts.
Figure 1. Assembly-level comparison of a virtual function call with and without CFI enabled.
For example, Figure 1 illustrates how a function that takes an object and calls a virtual function gets translated into assembly with and without CFI. For simplicity, this was compiled with -O0 to prevent compiler optimization. Without CFI enabled, it loads the object's vtable pointer and calls the function at the expected offset. With CFI enabled, it performs a fast-path first check to determine if the pointer falls within an expected range of addresses of compatible vtables. Failing that, execution falls through to a slow path that does a more extensive check for valid classes that are defined in other shared libraries. The slow path will abort execution if the vtable pointer points to an invalid target.
With control flow tightly restricted to a small set of legitimate targets, code-reuse attacks become harder to utilize and some memory corruption vulnerabilities become more difficult or even impossible to exploit.
In terms of performance impact, LLVM's CFI requires compiling with Link-Time Optimization (LTO). LTO preserves the LLVM bitcode representation of object files until link-time, which allows the compiler to better reason about what optimizations can be performed. Enabling LTO reduces the size of the final binary and improves performance, but increases compile time. In testing on Android, the combination of LTO and CFI results in negligible overhead to code size and performance; in a few cases both improved.
For more technical details about CFI and how other forward-control checks are handled, see the LLVM design documentation.
For Android P, CFI is enabled by default widely within the media frameworks and other security-critical components, such as NFC and Bluetooth. CFI kernel support has also been introduced into the Android common kernel when building with LLVM, providing the option to further harden the trusted computing base. This can be tested today on the HiKey reference boards.
The UndefinedBehaviorSanitizer's (UBSan) signed and unsigned integer overflow sanitization was first utilized when hardening the media stack in Android Nougat. This sanitization is designed to safely abort process execution if a signed or unsigned integer overflows by instrumenting arithmetic instructions which may overflow. The end result is the mitigation of an entire class of memory corruption and information disclosure vulnerabilities where the root cause is an integer overflow, such as the original Stagefright vulnerability.
Because of their success, we've expanded usage of these sanitizers in the media framework with each release. Improvements have been made to LLVM's integer overflow sanitizers to reduce the performance impact by using fewer instructions in ARM 32-bit and removing unnecessary checks. In testing, these improvements reduced the sanitizers' performance overhead by over 75% in Android's 32-bit libstagefright library for some codecs. Improved Android build system support, such as better diagnostics support, more sensible crashes, and globally sanitized integer overflow targets for testing have also expedited the rollout of these sanitizers.
We've prioritized enabling integer overflow sanitization in libraries where complex untrusted input is processed or where there have been security bulletin-level integer overflow vulnerabilities reported. As a result, in Android P the following libraries now benefit from this mitigation:
Moving forward, we're expanding our use of these mitigation technologies and we strongly encourage vendors to do the same with their customizations. More information about how to enable and test these options will be available soon on the Android Open Source Project.
Posted by Vishwath Mohan, Security Engineer
To keep users safe, most apps and devices have an authentication mechanism, or a way to prove that you're you. These mechanisms fall into three categories: knowledge factors, possession factors, and biometric factors. Knowledge factors ask for something you know (like a PIN or a password), possession factors ask for something you have (like a token generator or security key), and biometric factors ask for something you are (like your fingerprint, iris, or face).
Biometric authentication mechanisms are becoming increasingly popular, and it's easy to see why. They're faster than typing a password, easier than carrying around a separate security key, and they prevent one of the most common pitfalls of knowledge-factor based authentication—the risk of shoulder surfing.
As more devices incorporate biometric authentication to safeguard people's private information, we're improving biometrics-based authentication in Android P by:
Currently, biometric unlocks quantify their performance today with two metrics borrowed from machine learning (ML): False Accept Rate (FAR), and False Reject Rate (FRR).
In the case of biometrics, FAR measures how often a biometric model accidentally classifies an incorrect input as belonging to the target user—that is, how often another user is falsely recognized as the legitimate device owner. Similarly, FRR measures how often a biometric model accidentally classifies the user's biometric as incorrect—that is, how often a legitimate device owner has to retry their authentication. The first is a security concern, while the second is problematic for usability.
Both metrics do a great job of measuring the accuracy and precision of a given ML (or biometric) model when applied to random input samples. However, because neither metric accounts for an active attacker as part of the threat model, they do not provide very useful information about its resilience against attacks.
In Android 8.1, we introduced two new metrics that more explicitly account for an attacker in the threat model: Spoof Accept Rate (SAR) and Imposter Accept Rate (IAR). As their names suggest, these metrics measure how easily an attacker can bypass a biometric authentication scheme. Spoofing refers to the use of a known-good recording (e.g. replaying a voice recording or using a face or fingerprint picture), while impostor acceptance means a successful mimicking of another user's biometric (e.g. trying to sound or look like a target user).
We use the SAR/IAR metrics to categorize biometric authentication mechanisms as either strong or weak. Biometric authentication mechanisms with an SAR/IAR of 7% or lower are strong, and anything above 7% is weak. Why 7% specifically? Most fingerprint implementations have a SAR/IAR metric of about 7%, making this an appropriate standard to start with for other modalities as well. As biometric sensors and classification methods improve, this threshold can potentially be decreased in the future.
This binary classification is a slight oversimplification of the range of security that different implementations provide. However, it gives us a scalable mechanism (via the tiered authentication model) to appropriately scope the capabilities and the constraints of different biometric implementations across the ecosystem, based on the overall risk they pose.
While both strong and weak biometrics will be allowed to unlock a device, weak biometrics:
These measures are intended to allow weaker biometrics, while reducing the risk of unauthorized access.
Starting in Android P, developers can use the BiometricPrompt API to integrate biometric authentication into their apps in a device and biometric agnostic way. BiometricPrompt only exposes strong modalities, so developers can be assured of a consistent level of security across all devices their application runs on. A support library is also provided for devices running Android O and earlier, allowing applications to utilize the advantages of this API across more devices.
While applications can hook into BiometricPrompt directly for Android 9 and higher, developers should use the BiometricPrompt library to support the widest range of devices.
The API is intended to be easy to use, allowing the platform to select an appropriate biometric to authenticate with instead of forcing app developers to implement this logic themselves. Here's an example of how a developer might use it in their app:
Biometrics have the potential to both simplify and strengthen how we authenticate our digital identity, but only if they are designed securely, measured accurately, and implemented in a privacy-preserving manner.
We want Android to get it right across all three. So we're combining secure design principles, a more attacker-aware measurement methodology, and a common, easy to use biometrics API that allows developers to integrate authentication in a simple, consistent, and safe manner.
Acknowledgements: This post was developed in joint collaboration with Jim Miller.
Posted by Giles Hogben, Privacy Engineer and Milinda Perera, Software Engineer
Developers already use HTTPS to communicate with Firebase Cloud Messaging (FCM). The channel between FCM server endpoint and the device is encrypted with SSL over TCP. However, messages are not encrypted end-to-end (E2E) between the developer server and the user device unless developers take special measures.
To this end, we advise developers to use keys generated on the user device to encrypt push messages end-to-end. But implementing such E2E encryption has historically required significant technical knowledge and effort. That is why we are excited to announce the Capillary open source library which greatly simplifies the implementation of E2E-encryption for push messages between developer servers and users' Android devices.
We also added functionality for sending messages that can only be decrypted on devices that have recently been unlocked. This is designed to support decrypting messages on devices using File-Based Encryption (FBE): encrypted messages are cached in Device Encrypted (DE) storage and message decryption keys are stored in Android Keystore, requiring user authentication. This allows developers to specify messages with sensitive content, that remain encrypted in cached form until the user has unlocked and decrypted their device.
The library handles:
The library supports both RSA encryption with ECDSA authentication and Web Push encryption, allowing developers to re-use existing server-side code developed for sending E2E-encrypted Web Push messages to browser-based clients.
Along with the library, we are also publishing a demo app (at last, the Google privacy team has its own messaging app!) that uses the library to send E2E-encrypted FCM payloads from a gRPC-based server implementation.
You can find more technical details describing how we've architected and implemented the library and demo here.
Posted by Shawn Willden, Staff Software Engineer
Our smart devices, such as mobile phones and tablets, contain a wealth of personal information that needs to be kept safe. Google is constantly trying to find new and better ways to protect that valuable information on Android devices. From partnering with external researchers to find and fix vulnerabilities, to adding new features to the Android platform, we work to make each release and new device safer than the last. This post talks about Google's strategy for making the encryption on Google Pixel 2 devices resistant to various levels of attack—from platform, to hardware, all the way to the people who create the signing keys for Pixel devices.
We encrypt all user data on Google Pixel devices and protect the encryption keys in secure hardware. The secure hardware runs highly secure firmware that is responsible for checking the user's password. If the password is entered incorrectly, the firmware refuses to decrypt the device. This firmware also limits the rate at which passwords can be checked, making it harder for attackers to use a brute force attack.
To prevent attackers from replacing our firmware with a malicious version, we apply digital signatures. There are two ways for an attacker to defeat the signature checks and install a malicious replacement for firmware: find and exploit vulnerabilities in the signature-checking process or gain access to the signing key and get their malicious version signed so the device will accept it as a legitimate update. The signature-checking software is tiny, isolated, and vetted with extreme thoroughness. Defeating it is hard. The signing keys, however, must exist somewhere, and there must be people who have access to them.
In the past, device makers have focused on safeguarding these keys by storing the keys in secure locations and severely restricting the number of people who have access to them. That's good, but it leaves those people open to attack by coercion or social engineering. That's risky for the employees personally, and we believe it creates too much risk for user data.
To mitigate these risks, Google Pixel 2 devices implement insider attack resistance in the tamper-resistant hardware security module that guards the encryption keys for user data. This helps prevent an attacker who manages to produce properly signed malicious firmware from installing it on the security module in a lost or stolen device without the user's cooperation. Specifically, it is not possible to upgrade the firmware that checks the user's password unless you present the correct user password. There is a way to "force" an upgrade, for example when a returned device is refurbished for resale, but forcing it wipes the secrets used to decrypt the user's data, effectively destroying it.
The Android security team believes that insider attack resistance is an important element of a complete strategy for protecting user data. The Google Pixel 2 demonstrated that it's possible to protect users even against the most highly-privileged insiders. We recommend that all mobile device makers do the same. For help, device makers working to implement insider attack resistance can reach out to the Android security team through their Google contact.
Acknowledgements: This post was developed in joint collaboration with Paul Crowley, Senior Software Engineer
Posted by Sai Deep Tetali, Software Engineer, Google Play Protect
At Google I/O 2017, we introduced Google Play Protect, our comprehensive set of security services for Android. While the name is new, the smarts powering Play Protect have protected Android users for years.
Google Play Protect's suite of mobile threat protections are built into more than 2 billion Android devices, automatically taking action in the background. We're constantly updating these protections so you don't have to think about security: it just happens. Our protections have been made even smarter by adding machine learning elements to Google Play Protect.
Google Play Protect provides in-the-moment protection from potentially harmful apps (PHAs), but Google's protections start earlier.
Before they're published in Google Play, all apps are rigorously analyzed by our security systems and Android security experts. Thanks to this process, Android devices that only download apps from Google Play are 9 times less likely to get a PHA than devices that download apps from other sources.
After you install an app, Google Play Protect continues its quest to keep your device safe by regularly scanning your device to make sure all apps are behaving properly. If it finds an app that is misbehaving, Google Play Protect either notifies you, or simply removes the harmful app to keep your device safe.
Our systems scan over 50 billion apps every day. To keep on the cutting edge of security, we look for new risks in a variety of ways, such as identifying specific code paths that signify bad behavior, investigating behavior patterns to correlate bad apps, and reviewing possible PHAs with our security experts.
In 2016, we added machine learning as a new detection mechanism and it soon became a critical part of our systems and tools.
In the most basic terms, machine learning means training a computer algorithm to recognize a behavior. To train the algorithm, we give it hundreds of thousands of examples of that behavior.
In the case of Google Play Protect, we are developing algorithms that learn which apps are "potentially harmful" and which are "safe." To learn about PHAs, the machine learning algorithms analyze our entire catalog of applications. Then our algorithms look at hundreds of signals combined with anonymized data to compare app behavior across the Android ecosystem to find PHAs. They look for behavior common to PHAs, such as apps that attempt to interact with other apps on the device, access or share your personal data, download something without your knowledge, connect to phishing websites, or bypass built-in security features.
When we find apps exhibit similar malicious behavior, we group them into families. Visualizing these PHA families helps us uncover apps that share similarities to known bad apps, but have yet remained under our radar.
After we identify a new PHA, we confirm our findings with expert security reviews. If the app in question is a PHA, Google Play Protect takes action on the app and then we feed information about that PHA back into our algorithms to help find more PHAs.
So far, our machine learning systems have successfully detected 60.3% of the malware identified by Google Play Protect in 2017.
In 2018, we're devoting a massive amount of computing power and talent to create, maintain and improve these machine learning algorithms. We're constantly leveraging artificial intelligence and our highly skilled researchers and engineers from all across Google to find new ways to keep Android devices safe and secure. In addition to our talented team, we work with the foremost security experts and researchers from around the world. These researchers contribute even more data and insights to keep Google Play Protect on the cutting edge of mobile security.
To check out Google Play Protect, open the Google Play app and tap Play Protect in the left panel.
Acknowledgements: This work was developed in joint collaboration with Google Play Protect, Safe Browsing and Play Abuse teams with contributions from Andrew Ahn, Hrishikesh Aradhye, Daniel Bali, Hongji Bao, Yajie Hu, Arthur Kaiser, Elena Kovakina, Salvador Mandujano, Melinda Miller, Rahul Mishra, Damien Octeau, Sebastian Porst, Chuangang Ren, Monirul Sharif, Sri Somanchi, Sai Deep Tetali, Zhikun Wang, and Mo Yu.
Posted by Nate Fischer, Software Engineer
Since 2007, Google Safe Browsing has been protecting users across the web from phishing and malware attacks. It protects over three billion devices from an increasing number of threats, now also including unwanted software across desktop and mobile platforms. Today, we're announcing that Google Play Protect is bringing Safe Browsing to WebView by default, starting in April 2018 with the release of WebView 66.
Developers of Android apps using WebView no longer have to make any changes to benefit from this protection. Safe Browsing in WebView has been available since Android 8.0 (API level 26), using the same underlying technology as Chrome on Android. When Safe Browsing is triggered, the app will present a warning and receive a network error. Apps built for API level 27 and above can customize this behavior with new APIs for Safe Browsing.
An example of a warning shown when Safe Browsing detects a dangerous site. The style and content of the warning will vary depending on the size of the WebView.
You can learn more about customizing and controlling Safe Browsing in the Android API documentation, and you can test your application today by visiting the Safe Browsing test URL (chrome://safe-browsing/match?type=malware) while using the current WebView beta.
Posted by Erik Kline, Android software engineer, and Ben Schwartz, Jigsaw software engineer
The first step of almost every connection on the internet is a DNS query. A client, such as a smartphone, typically uses a DNS server provided by the Wi-Fi or cellular network. The client asks this DNS server to convert a domain name, like www.google.com, into an IP address, like 2607:f8b0:4006:80e::2004. Once the client has the IP address, it can connect to its intended destination.
When the DNS protocol was designed in the 1980s, the internet was a much smaller, simpler place. For the past few years, the Internet Engineering Task Force (IETF) has worked to define a new DNS protocol that provides users with the latest protections for security and privacy. The protocol is called "DNS over TLS" (standardized as RFC 7858).
Like HTTPS, DNS over TLS uses the TLS protocol to establish a secure channel to the server. Once the secure channel is established, DNS queries and responses can't be read or modified by anyone else who might be monitoring the connection. (The secure channel only applies to DNS, so it can't protect users from other kinds of security and privacy violations.)
The Android P Developer Preview includes built-in support for DNS over TLS. We added a Private DNS mode to the Network & internet settings.
By default, devices automatically upgrade to DNS over TLS if a network's DNS server supports it. But users who don't want to use DNS over TLS can turn it off.
Users can enter a hostname if they want to use a private DNS provider. Android then sends all DNS queries over a secure channel to this server or marks the network as "No internet access" if it can't reach the server. (For testing purposes, see this community-maintained list of compatible servers.)
DNS over TLS mode automatically secures the DNS queries from all apps on the system. However, apps that perform their own DNS queries, instead of using the system's APIs, must ensure that they do not send insecure DNS queries when the system has a secure connection. Apps can get this information using a new API: LinkProperties.isPrivateDnsActive().
LinkProperties.isPrivateDnsActive()
With the Android P Developer Preview, we're proud to present built-in support for DNS over TLS. In the future, we hope that all operating systems will include secure transports for DNS, to provide better protection and privacy for all users on every new connection.
Posted by Chad Brubaker, Senior Software Engineer Android Security
Android is committed to keeping users, their devices, and their data safe. One of the ways that we keep data safe is by protecting all data that enters or leaves an Android device with Transport Layer Security (TLS) in transit. As we announced in our Android P developer preview, we're further improving these protections by preventing apps that target Android P from allowing unencrypted connections by default.
This follows a variety of changes we've made over the years to better protect Android users.To prevent accidental unencrypted connections, we introduced the android:usesCleartextTraffic manifest attribute in Android Marshmallow. In Android Nougat, we extended that attribute by creating the Network Security Config feature, which allows apps to indicate that they do not intend to send network traffic without encryption. In Android Nougat and Oreo, we still allowed cleartext connections.
android:usesCleartextTraffic
If your app uses TLS for all connections then you have nothing to do. If not, update your app to use TLS to encrypt all connections. If you still need to make cleartext connections, keep reading for some best practices.
Android considers all networks potentially hostile and so encrypting traffic should be used at all times, for all connections. Mobile devices are especially at risk because they regularly connect to many different networks, such as the Wi-Fi at a coffee shop.
All traffic should be encrypted, regardless of content, as any unencrypted connections can be used to inject content, increase attack surface for potentially vulnerable client code, or track the user. For more information, see our past blog post and Developer Summit talk.
No, it's not.
Once your server supports TLS, simply change the URLs in your app and server responses from http:// to https://. Your HTTP stack handles the TLS handshake without any more work.
If you are making sockets yourself, use an SSLSocketFactory instead of a SocketFactory. Take extra care to use the socket correctly as SSLSocket doesn't perform hostname verification. Your app needs to do its own hostname verification, preferably by calling getDefaultHostnameVerifier() with the expected hostname. Further, beware that HostnameVerifier.verify() doesn't throw an exception on error but instead returns a boolean result that you must explicitly check.
getDefaultHostnameVerifier()
HostnameVerifier.verify()
While you should use TLS for all connections, it's possibly that you need to use cleartext traffic for legacy reasons, such as connecting to some servers. To do this, change your app's network security config to allow those connections.
We've included a couple example configurations. See the network security config documentation for a bit more help.
If you need to allow connections to a specific domain or set of domains, you can use the following config as a guide:
<network-security-config> <domain-config cleartextTrafficPermitted="true"> <domain includeSubdomains="true">insecure.example.com</domain> <domain includeSubdomains="true">insecure.cdn.example.com</domain> </domain-config> </network-security-config>
If your app supports opening arbitrary content from URLs over insecure connections, you should disable cleartext connections to your own services while supporting cleartext connections to arbitrary hosts. Keep in mind that you should be cautious about the data received over insecure connections as it could have been tampered with in transit.
<network-security-config> <domain-config cleartextTrafficPermitted="false"> <domain includeSubdomains="true">example.com</domain> <domain includeSubdomains="true">cdn.example2.com</domain> </domain-config> <base-config cleartextTrafficPermitted="true" /> </network-security-config>
If your library directly creates secure/insecure connections, make sure that it honors the app's cleartext settings by checking isCleartextTrafficPermitted before opening any cleartext connection.
Our team's goal is simple: secure more than two billion Android devices. It's our entire focus, and we're constantly working to improve our protections to keep users safe.
Today, we're releasing our fourth annual Android security year in review. We compile these reports to help educate the public about the many different layers of Android security, and also to hold ourselves accountable so that anyone can track our security work over time.
We saw some really positive momentum last year and this post includes some, but not nearly all, of the major moments from 2017. To dive into all the details, you can read the full report at: g.co/AndroidSecurityReport2017
In May, we announced Google Play Protect, a new home for the suite of Android security services on nearly two billion devices. While many of Play Protect's features had been securing Android devices for years, we wanted to make these more visible to help assure people that our security protections are constantly working to keep them safe.
Play Protect's core objective is to shield users from Potentially Harmful Apps, or PHAs. Every day, it automatically reviews more than 50 billion apps, other potential sources of PHAs, and devices themselves and takes action when it finds any.
Play Protect uses a variety of different tactics to keep users and their data safe, but the impact of machine learning is already quite significant: 60.3% of all Potentially Harmful Apps were detected via machine learning, and we expect this to increase in the future.
Play Protect automatically checks Android devices for PHAs at least once every day, and users can conduct an additional review at any time for some extra peace of mind. These automatic reviews enabled us to remove nearly 39 million PHAs last year.
We also update Play Protect to respond to trends that we detect across the ecosystem. For instance, we recognized that nearly 35% of new PHA installations were occurring when a device was offline or had lost network connectivity. As a result, in October 2017, we enabled offline scanning in Play Protect, and have since prevented 10 million more PHA installs.
Devices that downloaded apps exclusively from Google Play were nine times less likely to get a PHA than devices that downloaded apps from other sources. And these security protections continue to improve, partially because of Play Protect's increased visibility into newly submitted apps to Play. It reviewed 65% more Play apps compared to 2016.
Play Protect also doesn't just secure Google Play—it helps protect the broader Android ecosystem as well. Thanks in large part to Play Protect, the installation rates of PHAs from outside of Google Play dropped by more than 60%.
While Google Play Protect is a great shield against harmful PHAs, we also partner with device manufacturers to make sure that the version of Android running on user devices is up-to-date and secure.
Throughout the year, we worked to improve the process for releasing security updates, and 30% more devices received security patches than in 2016. Furthermore, no critical security vulnerabilities affecting the Android platform were publicly disclosed without an update or mitigation available for Android devices. This was possible due to the Android Security Rewards Program, enhanced collaboration with the security researcher community, coordination with industry partners, and built-in security features of the Android platform.
We introduced a slew of new security features in Android Oreo: making it safer to get apps, dropping insecure network protocols, providing more user control over identifiers, hardening the kernel, and more.
We highlighted many of these over the course of the year, but some may have flown under the radar. For example, we updated the overlay API so that apps can no longer block the entire screen and prevent you from dismissing them, a common tactic employed by ransomware.
We've long said it, but it remains truer than ever: Android's openness helps strengthen our security protections. For years, the Android ecosystem has benefitted from researchers' findings, and 2017 was no different.
We continued to see great momentum with our Android Security Rewards program: we paid researchers $1.28 million, totalling more than two million dollars since the start of the program. We also increased our top-line payouts for exploits that compromise TrustZone or Verified Boot from $50,000 to $200,000, and remote kernel exploits from $30,000 to $150,000.
In parallel, we also introduced Google Play Security Rewards program and offered a bonus bounty to developers that discover and disclose select critical vulnerabilities in apps hosted on Play to their developers.
Our teams also participated in external vulnerability discovery and disclosure competitions, such as Mobile Pwn2Own. At the 2017 Mobile Pwn2Own competition, no exploits successfully compromised the Google Pixel. And of the exploits demonstrated against devices running Android, none could be reproduced on a device running unmodified Android source code from the Android Open Source Project (AOSP).
We're pleased to see the positive momentum behind Android security, and we'll continue our work to improve our protections this year, and beyond. We will never stop our work to ensure the security of Android users.
Play Console
