Starting March 27, 2025, we recommend using android-latest-release instead of aosp-main to build and contribute to AOSP. For more information, see Changes to AOSP.

Security enhancements
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Android continuously improves its security abilities and offerings. See the lists of enhancements by release in the left navigation.

Android 14

Every Android release includes dozens of security enhancements to protect users. Here are some of the major security enhancements available in Android 14:

Hardware-assisted AddressSanitizer (HWASan), introduced in Android 10, is a memory error detection tool similar to AddressSanitizer. Android 14 brings significant improvements to HWASan. Learn how it helps prevent bugs from making it into Android releases, HWAddressSanitizer
In Android 14, starting with apps that share location data with third-parties, the system runtime permission dialog now includes a clickable section that highlights the app's data-sharing practices, including information such as why an app may decide to share data with third parties.
Android 12 introduced an option to disable 2G support at the modem level, which protects users from the inherent security risk from 2G's obsolete security model. Recognizing how critical disabling 2G could be for enterprise customers, Android 14 enables this security feature in Android Enterprise, introducing support for IT admins to restrict the ability of a managed device to downgrade to 2G connectivity.
Added support to reject null-ciphered cellular connections, ensuring that circuit-switched voice and SMS traffic is always encrypted and protected from passive over-the-air interception. Learn more about Android's program to harden cellular connectivity.
Added support for multiple IMEIs
Since Android 14, AES-HCTR2 is the preferred mode of filenames encryption for devices with accelerated cryptography instructions.
Cellular connectivity
Documentation added for Android Safety Center
If your app targets Android 14 and uses Dynamic Code Loading (DCL), all dynamically-loaded files must be marked as read-only. Otherwise, the system throws an exception. We recommend that apps avoid dynamically loading code whenever possible, as doing so greatly increases the risk that an app can be compromised by code injection or code tampering.

Check out our full AOSP release notes and the Android Developer features and changes list.

Android 13

Every Android release includes dozens of security enhancements to protect users. Here are some of the major security enhancements available in Android 13:

Android 13 adds multi-document presentation support. This new Presentation Session interface enables an app to do a multi-document presentation, something which isn't possible with the existing API. For further information, refer to Identity Credential
In Android 13, intents originating from external apps are delivered to an exported component if and only if the intents match their declared intent-filter elements.
Open Mobile API (OMAPI) is a standard API used to communicate with a device's Secure Element. Before Android 13, only apps and framework modules had access to this interface. By converting it to a vendor stable interface, HAL modules are also capable of communicating with the secure elements through the OMAPI service. For more information, see OMAPI Vendor Stable Interface.
As of Android 13-QPR, shared UIDs are deprecated. Users of Android 13 or higher should put the line `android:sharedUserMaxSdkVersion="32"` in their manifest. This entry prevents new users from getting a shared UID. For further information on UIDs, see App signing.
Android 13 added support Keystore symmetric cryptographic primitives such as AES (Advanced Encryption Standard), HMAC (Keyed-Hash Message Authentication Code), and asymmetric cryptographic algorithms (including Elliptic Curve, RSA2048, RSA4096, and Curve 25519)
Android 13 (API level 33) and higher supports a runtime permission for sending non-exempt notifications from an app. This gives users control over which permission notifications they see.
Added per-use prompt for apps requesting access to all device logs, giving users the ability to allow or deny access.
introduced the Android Virtualization Framework (AVF), which brings together different hypervisors under one framework with standardized APIs. It provides secure and private execution environments for executing workloads isolated by hypervisor.
Introduced APK signature scheme v3.1 All new key rotations that use apksigner use the v3.1 signature scheme by default to target rotation for Android 13 and higher.

Check out our full AOSP release notes and the Android Developer features and changes list.

Android 12

Every Android release includes dozens of security enhancements to protect users. Here are some of the major security enhancements available in Android 12:

Android 12 introduces the BiometricManager.Strings API, which provides localized strings for apps that use BiometricPrompt for authentication. These strings are intended to be device-aware and provide more specificity about which authentication types might be used. Android 12 also includes support for under-display fingerprint sensors
Support added for under-display fingerprint sensors
Introduction of the Fingerprint Android Interface Definition Language (AIDL)
Support for new Face AIDL
Introduction of Rust as a language for platform development
The option for users to grant access only to their approximate location added
Added Privacy indicators on the status bar when an app is using the camera or microphone
Android's Private Compute Core (PCC)
Added an option to disable 2G support

Android 11

Every Android release includes dozens of security enhancements to protect users. For a list of some of the major security enhancements available in Android 11, see the Android Release Notes.

Android 10

Every Android release includes dozens of security enhancements to protect users. Android 10 includes several security and privacy enhancements. See the Android 10 release notes for a complete list of changes in Android 10.

Security

BoundsSanitizer

Android 10 deploys BoundsSanitizer (BoundSan) in Bluetooth and codecs. BoundSan uses UBSan's bounds sanitizer. This mitigation is enabled on a per-module level. It helps keep critical components of Android secure and shouldn't be disabled. BoundSan is enabled in the following codecs:

libFLAC
libavcdec
libavcenc
libhevcdec
libmpeg2
libopus
libvpx
libspeexresampler
libvorbisidec
libaac
libxaac

Execute-only memory

By default, executable code sections for AArch64 system binaries are marked execute-only (nonreadable) as a hardening mitigation against just-in-time code reuse attacks. Code that mixes data and code together and code that purposefully inspects these sections (without first remapping the memory segments as readable) no longer functions. Apps with a target SDK of Android 10 (API level 29 or higher) are impacted if the app attempts to read code sections of execute-only memory (XOM) enabled system libraries in memory without first marking the section as readable.

Extended access

Trust agents, the underlying mechanism used by tertiary authentication mechanisms such as Smart Lock, can only extend unlock in Android 10. Trust agents can no longer unlock a locked device and can only keep a device unlocked for a maximum of four hours.

Face authentication

Face authentication allows users to unlock their device simply by looking at the front of their device. Android 10 adds support for a new face authentication stack that can securely process camera frames, preserving security and privacy during face authentication on supported hardware. Android 10 also provides an easy way for security-compliant implementations to enable app integration for transactions such as online banking or other services.

Integer Overflow Sanitization

Android 10 enables Integer Overflow Sanitization (IntSan) in software codecs. Ensure that playback performance is acceptable for any codecs that aren't supported in the device's hardware. IntSan is enabled in the following codecs:

libFLAC
libavcdec
libavcenc
libhevcdec
libmpeg2
libopus
libvpx
libspeexresampler
libvorbisidec

Modular system components

Android 10 modularizes some Android system components and enables them to be updated outside of the normal Android release cycle. Some modules include:

OEMCrypto

Android 10 uses OEMCrypto API version 15.

Scudo

Scudo is a dynamic user-mode memory allocator designed to be more resilient against heap-related vulnerabilities. It provides the standard C allocation and deallocation primitives, as well as the C++ primitives.

ShadowCallStack

ShadowCallStack (SCS) is an LLVM instrumentation mode that protects against return address overwrites (like stack buffer overflows) by saving a function's return address to a separately allocated ShadowCallStack instance in the function prolog of nonleaf functions and loading the return address from the ShadowCallStack instance in the function epilog.

WPA3 and Wi-Fi Enhanced Open

Android 10 adds support for the Wi-Fi Protected Access 3 (WPA3) and Wi-Fi Enhanced Open security standards to provide better privacy and robustness against known attacks.

Privacy

App access when targeting Android 9 or lower

If your app runs on Android 10 or higher but targets Android 9 (API level 28) or lower, the platform applies the following behavior:

If your app declares a <uses-permission> element for either ACCESS_FINE_LOCATION or ACCESS_COARSE_LOCATION, the system automatically adds a <uses-permission> element for ACCESS_BACKGROUND_LOCATION during installation.
If your app requests either ACCESS_FINE_LOCATION or ACCESS_COARSE_LOCATION, the system automatically adds ACCESS_BACKGROUND_LOCATION to the request.

Background activity restrictions

Starting in Android 10, the system places restrictions on starting activities from the background. This behavior change helps minimize interruptions for the user and keeps the user more in control of what's shown on their screen. As long as your app starts activities as a direct result of user interaction, your app most likely isn't affected by these restrictions.
To learn more about the recommended alternative to starting activities from the background, see the guide on how to alert users of time-sensitive events in your app.

Camera metadata

Android 10 changes the breadth of information that the getCameraCharacteristics() method returns by default. In particular, your app must have the CAMERA permission in order to access potentially device-specific metadata that is included in this method's return value.
To learn more about these changes, see the section about camera fields that require permission.

Clipboard data

Unless your app is the default input method editor (IME) or is the app that currently has focus, your app cannot access clipboard data on Android 10 or higher.

Device location

To support the additional control that users have over an app's access to location information, Android 10 introduces the ACCESS_BACKGROUND_LOCATION permission.
Unlike the ACCESS_FINE_LOCATION and ACCESS_COARSE_LOCATION permissions, the ACCESS_BACKGROUND_LOCATION permission only affects an app's access to location when it runs in the background. An app is considered to be accessing location in the background unless one of the following conditions is satisfied:

An activity belonging to the app is visible.
The app is running a foreground service that has declared a foreground service type of location.
To declare the foreground service type for a service in your app, set your app's targetSdkVersion or compileSdkVersion to 29 or higher. Learn more about how foreground services can continue user-initiated actions that require access to location.

External storage

By default, apps targeting Android 10 and higher are given scoped access into external storage, or scoped storage. Such apps can see the following types of files within an external storage device without needing to request any storage-related user permissions:

Files in the app-specific directory, accessed using getExternalFilesDir().
Photos, videos, and audio clips that the app created from the media store.

To learn more about scoped storage, as well as how to share, access, and modify files that are saved on external storage devices, see the guides on how to manage files in external storage and access and modify media files.

MAC address randomization

On devices that run Android 10 or higher, the system transmits randomized MAC addresses by default.
If your app handles an enterprise use case, the platform provides APIs for several operations related to MAC addresses:

Obtain randomized MAC address: Device owner apps and profile owner apps can retrieve the randomized MAC address assigned to a specific network by calling getRandomizedMacAddress().
Obtain actual, factory MAC address: Device owner apps can retrieve a device's actual hardware MAC address by calling getWifiMacAddress(). This method is useful for tracking fleets of devices.

Non-resettable device identifiers

Starting in Android 10, apps must have the READ_PRIVILEGED_PHONE_STATE privileged permission in order to access the device's non-resettable identifiers, which include both IMEI and serial number.

Build
- getSerial()
TelephonyManager
- getImei()
- getDeviceId()
- getMeid()
- getSimSerialNumber()
- getSubscriberId()

If your app doesn't have the permission and you try asking for information about non-resettable identifiers anyway, the platform's response varies based on target SDK version:

If your app targets Android 10 or higher, a SecurityException occurs.
If your app targets Android 9 (API level 28) or lower, the method returns null or placeholder data if the app has the READ_PHONE_STATE permission. Otherwise, a SecurityException occurs.

Physical activity recognition

Android 10 introduces the android.permission.ACTIVITY_RECOGNITION runtime permission for apps that need to detect the user's step count or classify the user's physical activity, such as walking, biking, or moving in a vehicle. This is designed to give users visibility of how device sensor data is used in Settings.
Some libraries within Google Play services, such as the Activity Recognition API and the Google Fit API, don't provide results unless the user has granted your app this permission.
The only built-in sensors on the device that require you to declare this permission are the step counter and step detector sensors.
If your app targets Android 9 (API level 28) or lower, the system auto-grants the android.permission.ACTIVITY_RECOGNITION permission to your app, as needed, if your app satisfies each of the following conditions:

The manifest file includes the com.google.android.gms.permission.ACTIVITY_RECOGNITION permission.
The manifest file doesn't include the android.permission.ACTIVITY_RECOGNITION permission.

If the system-auto grants the android.permission.ACTIVITY_RECOGNITION permission, your app retains the permission after you update your app to target Android 10. However, the user can revoke this permission at any time in system settings.

/proc/net filesystem restrictions

On devices that run Android 10 or higher, apps cannot access /proc/net, which includes information about a device's network state. Apps that need access to this information, such as VPNs, should use the NetworkStatsManager or ConnectivityManager class.

Permission groups removed from UI

As of Android 10, apps cannot look up how permissions are grouped in the UI.

Removal of contacts affinity

Starting in Android 10, the platform doesn't keep track of contacts affinity information. As a result, if your app conducts a search on the user's contacts, the results aren't ordered by frequency of interaction.
The guide about ContactsProvider contains a notice describing the specific fields and methods that are obsolete on all devices starting in Android 10.

Restricted access to screen contents

To protect users' screen contents, Android 10 prevents silent access to the device's screen contents by changing the scope of the READ_FRAME_BUFFER, CAPTURE_VIDEO_OUTPUT, and CAPTURE_SECURE_VIDEO_OUTPUT permissions. As of Android 10, these permissions are signature-access only.
Apps that need to access the device's screen contents should use the MediaProjection API, which displays a prompt asking the user to provide consent.

USB device serial number

If your app targets Android 10 or higher, your app cannot read the serial number until the user has granted your app permission to access the USB device or accessory.
To learn more about working with USB devices, see the guide on how to configure USB hosts.

Wi-Fi

Apps targeting Android 10 or higher cannot enable or disable Wi-Fi. The WifiManager.setWifiEnabled() method always returns false.
If you need to prompt users to enable and disable Wi-Fi, use a settings panel.

Restrictions on direct access to configured Wi-Fi networks

To protect user privacy, manual configuration of the list of Wi-Fi networks is restricted to system apps and device policy controllers (DPCs). A given DPC can be either the device owner or the profile owner.
If your app targets Android 10 or higher, and it isn't a system app or a DPC, then the following methods don't return useful data:

The getConfiguredNetworks() method always returns an empty list.
Each network operation method that returns an integer value—addNetwork() and updateNetwork()—always returns -1.
Each network operation that returns a boolean value—removeNetwork(), reassociate(), enableNetwork(), disableNetwork(), reconnect(), and disconnect()—always returns false.

Android 9

Every Android release includes dozens of security enhancements to protect users. For a list of some of the major security enhancements available in Android 9, see the Android Release Notes.

Android 8

Every Android release includes dozens of security enhancements to protect users. Here are some of the major security enhancements available in Android 8.0:

Encryption. Added support to evict key in work profile.
Verified Boot. Added Android Verified Boot (AVB). Verified Boot codebase supporting rollback protection for use in boot loaders added to AOSP. Recommend bootloader support for rollback protection for the HLOS. Recommend boot loaders can only be unlocked by user physically interacting with the device.
Lock screen. Added support for using tamper-resistant hardware to verify lock screen credential.
KeyStore. Required key attestation for all devices that ship with Android 8.0+. Added ID attestation support to improve Zero Touch Enrollment.
Sandboxing. More tightly sandboxed many components using Project Treble's standard interface between framework and device-specific components. Applied seccomp filtering to all untrusted apps to reduce the kernel's attack surface. WebView is now run in an isolated process with very limited access to the rest of the system.
Kernel hardening. Implemented hardened usercopy, PAN emulation, read-only after init, and KASLR.
Userspace hardening. Implemented CFI for the media stack. App overlays can no longer cover system-critical windows and users have a way to dismiss them.
Streaming OS update. Enabled updates on devices that are are low on disk space.
Install unknown apps. Users must grant permission to install apps from a source that isn't a first-party app store.
Privacy. Android ID (SSAID) has a different value for each app and each user on the device. For web browser apps, Widevine Client ID returns a different value for each app package name and web origin. net.hostname is now empty and the dhcp client no longer sends a hostname. android.os.Build.SERIAL has been replaced with the Build.SERIAL API which is protected behind a user-controlled permission. Improved MAC address randomization in some chipsets.

Android 7

Every Android release includes dozens of security enhancements to protect users. Here are some of the major security enhancements available in Android 7.0:

File-based encryption. Encrypting at the file level, instead of encrypting the entire storage area as a single unit, better isolates and protects individual users and profiles (such as personal and work) on a device.
Direct Boot. Enabled by file-based encryption, Direct Boot allows certain apps such as alarm clock and accessibility features to run when device is powered on but not unlocked.
Verified Boot. Verified Boot is now strictly enforced to prevent compromised devices from booting; it supports error correction to improve reliability against non-malicious data corruption.
SELinux. Updated SELinux configuration and increased seccomp coverage further locks down the Application Sandbox and reduces attack surface.
Library load-order randomization and improved ASLR. Increased randomness makes some code-reuse attacks less reliable.
Kernel hardening. Added additional memory protection for newer kernels by marking portions of kernel memory as read-only, restricting kernel access to userspace addresses and further reducing the existing attack surface.
APK signature scheme v2. Introduced a whole-file signature scheme that improves verification speed and strengthens integrity guarantees.
Trusted CA store. To make it easier for apps to control access to their secure network traffic, user-installed certificate authorities and those installed through Device Admin APIs are no longer trusted by default for apps targeting API Level 24+. Additionally, all new Android devices must ship with the same trusted CA store.
Network Security Config. Configure network security and TLS through a declarative configuration file.

Android 6

Every Android release includes dozens of security enhancements to protect users. Here are some of the major security enhancements available in Android 6.0:

Runtime Permissions. Apps request permissions at runtime instead of being granted at App install time. Users can toggle permissions on and off for both M and pre-M apps.
Verified Boot. A set of cryptographic checks of system software are conducted prior to execution to ensure the phone is healthy from the bootloader all the way up to the operating system.
Hardware-Isolated Security. New Hardware Abstraction Layer (HAL) used by Fingerprint API, Lockscreen, Device Encryption, and Client Certificates to protect keys against kernel compromise and/or local physical attacks
Fingerprints. Devices can now be unlocked with just a touch. Developers can also take advantage of new APIs to use fingerprints to lock and unlock encryption keys.
SD Card Adoption. Removable media can be adopted to a device and expand available storage for app local data, photos, videos, etc., but still be protected by block-level encryption.
Clear Text Traffic. Developers can use a new StrictMode to make sure their app doesn't use cleartext.
System Hardening. Hardening of the system via policies enforced by SELinux. This offers better isolation between users, IOCTL filtering, reduce threat of exposed services, further tightening of SELinux domains, and extremely limited /proc access.
USB Access Control: Users must confirm to allow USB access to files, storage, or other functionality on the phone. Default is now charge only with access to storage requiring explicit approval from the user.

Android 5

5.0

Every Android release includes dozens of security enhancements to protect users. Here are some of the major security enhancements available in Android 5.0:

Encrypted by default. On devices that ship with L out-of-the-box, full disk encryption is enabled by default to improve protection of data on lost or stolen devices. Devices that update to L can be encrypted in Settings > Security .
Improved full disk encryption. The user password is protected against brute-force attacks using scrypt and, where available, the key is bound to the hardware keystore to prevent off-device attacks. As always, the Android screen lock secret and the device encryption key are not sent off the device or exposed to any application.
Android sandbox reinforced with SELinux . Android now requires SELinux in enforcing mode for all domains. SELinux is a mandatory access control (MAC) system in the Linux kernel used to augment the existing discretionary access control (DAC) security model. This new layer provides additional protection against potential security vulnerabilities.
Smart Lock. Android now includes trustlets that provide more flexibility for unlocking devices. For example, trustlets can allow devices to be unlocked automatically when close to another trusted device (through NFC, Bluetooth) or being used by someone with a trusted face.
Multi user, restricted profile, and guest modes for phones and tablets. Android now provides for multiple users on phones and includes a guest mode that can be used to provide easy temporary access to your device without granting access to your data and apps.
Updates to WebView without OTA. WebView can now be updated independent of the framework and without a system OTA. This allows for faster response to potential security issues in WebView.
Updated cryptography for HTTPS and TLS/SSL. TLSv1.2 and TLSv1.1 is now enabled, Forward Secrecy is now preferred, AES-GCM is now enabled, and weak cipher suites (MD5, 3DES, and export cipher suites) are now disabled. See https://developer.android.com/reference/javax/net/ssl/SSLSocket.html for more details.
non-PIE linker support removed. Android now requires all dynamically linked executables to support PIE (position-independent executables). This enhances Android's address space layout randomization (ASLR) implementation.
FORTIFY_SOURCE improvements. The following libc functions now implement FORTIFY_SOURCE protections: stpcpy(), stpncpy(), read(), recvfrom(), FD_CLR(), FD_SET(), and FD_ISSET(). This provides protection against memory-corruption vulnerabilities involving those functions.
Security Fixes. Android 5.0 also includes fixes for Android-specific vulnerabilities. Information about these vulnerabilities has been provided to Open Handset Alliance members, and fixes are available in Android Open Source Project. To improve security, some devices with earlier versions of Android may also include these fixes.

Android 4 and lower

Every Android release includes dozens of security enhancements to protect users. The following are some of the security enhancements available in Android 4.4:

Android sandbox reinforced with SELinux. Android now uses SELinux in enforcing mode. SELinux is a mandatory access control (MAC) system in the Linux kernel used to augment the existing discretionary access control (DAC) based security model. This provides additional protection against potential security vulnerabilities.
Per User VPN. On multi-user devices, VPNs are now applied per user. This can allow a user to route all network traffic through a VPN without affecting other users on the device.
ECDSA Provider support in AndroidKeyStore. Android now has a keystore provider that allows use of ECDSA and DSA algorithms.
Device Monitoring Warnings. Android provides users with a warning if any certificate has been added to the device certificate store that could allow monitoring of encrypted network traffic.
FORTIFY_SOURCE. Android now supports FORTIFY_SOURCE level 2, and all code is compiled with these protections. FORTIFY_SOURCE has been enhanced to work with clang.
Certificate Pinning. Android 4.4 detects and prevents the use of fraudulent Google certificates used in secure SSL/TLS communications.
Security Fixes. Android 4.4 also includes fixes for Android-specific vulnerabilities. Information about these vulnerabilities has been provided to Open Handset Alliance members and fixes are available in Android Open Source Project. To improve security, some devices with earlier versions of Android may also include these fixes.

Every Android release includes dozens of security enhancements to protect users. The following are some of the security enhancements available in Android 4.3:

Android sandbox reinforced with SELinux. This release strengthens the Android sandbox using the SELinux mandatory access control system (MAC) in the Linux kernel. SELinux reinforcement is invisible to users and developers, and adds robustness to the existing Android security model while maintaining compatibility with existing apps. To ensure continued compatibility this release allows the use of SELinux in a permissive mode. This mode logs any policy violations, but will not break apps or affect system behavior.
No setuid or setgid programs. Added support for filesystem capabilities to Android system files and removed all setuid or setgid programs. This reduces root attack surface and the likelihood of potential security vulnerabilities.
ADB authentication. Starting in Android 4.2.2, connections to ADB are authenticated with an RSA keypair. This prevents unauthorized use of ADB where the attacker has physical access to a device.
Restrict Setuid from Android Apps. The /system partition is now mounted nosuid for zygote-spawned processes, preventing Android apps from executing setuid programs. This reduces root attack surface and the likelihood of potential security vulnerabilities.
Capability bounding. Android zygote and ADB now use prctl(PR_CAPBSET_DROP) to drop unnecessary capabilities prior to executing apps. This prevents Android apps and apps launched from the shell from acquiring privileged capabilities.
AndroidKeyStore Provider. Android now has a keystore provider that allows apps to create exclusive use keys. This provides apps with an API to create or store private keys that cannot be used by other apps.
KeyChain isBoundKeyAlgorithm. Keychain API now provides a method (isBoundKeyType) that allows apps to confirm that system-wide keys are bound to a hardware root of trust for the device. This provides a place to create or store private keys that can't be exported off the device, even in the event of a root compromise.
NO_NEW_PRIVS. Android zygote now uses prctl(PR_SET_NO_NEW_PRIVS) to block addition of new privileges prior to execution app code. This prevents Android apps from performing operations that can elevate privileges through execve. (This requires Linux kernel version 3.5 or greater).
FORTIFY_SOURCE enhancements. Enabled FORTIFY_SOURCE on Android x86 and MIPS and fortified strchr(), strrchr(), strlen(), and umask() calls. This can detect potential memory corruption vulnerabilities or unterminated string constants.
Relocation protections. Enabled read only relocations (relro) for statically linked executables and removed all text relocations in Android code. This provides defense in depth against potential memory corruption vulnerabilities.
Improved EntropyMixer. EntropyMixer now writes entropy at shutdown or reboot, in addition to periodic mixing. This allows retention of all entropy generated while devices are powered on, and is especially useful for devices that are rebooted immediately after provisioning.
Security fixes. Android 4.3 also includes fixes for Android-specific vulnerabilities. Information about these vulnerabilities has been provided to Open Handset Alliance members and fixes are available in Android Open Source Project. To improve security, some devices with earlier versions of Android may also include these fixes.

Android provides a multi-layered security model described in the Android Security Overview. Each update to Android includes dozens of security enhancements to protect users. The following are some of the security enhancements introduced in Android 4.2:

App verification: Users can choose to enable Verify Apps and have apps screened by an app verifier, prior to installation. App verification can alert the user if they try to install an app that might be harmful; if an app is especially bad, it can block installation.
More control of premium SMS: Android provides a notification if an app attempts to send SMS to a short code that uses premium services that might cause additional charges. The user can choose whether to allow the app to send the message or block it.
Always-on VPN: VPN can be configured so that apps won't have access to the network until a VPN connection is established. This prevents apps from sending data across other networks.
Certificate pinning: The Android core libraries now support certificate pinning. Pinned domains receive a certificate validation failure if the certificate doesn't chain to a set of expected certificates. This protects against possible compromise of certificate authorities.
Improved display of Android permissions: Permissions are organized into groups that are more easily understood by users. During review of the permissions, the user can click on the permission to see more detailed information about the permission.
installd hardening: The installd daemon does not run as the root user, reducing potential attack surface for root privilege escalation.
init script hardening: init scripts now apply O_NOFOLLOW semantics to prevent symlink related attacks.
FORTIFY_SOURCE: Android now implements FORTIFY_SOURCE. This is used by system libraries and apps to prevent memory corruption.
ContentProvider default configuration: Apps that target API level 17 have export set to false by default for each Content Provider, reducing default attack surface for apps.
Cryptography: Modified the default implementations of SecureRandom and Cipher.RSA to use OpenSSL. Added SSL Socket support for TLSv1.1 and TLSv1.2 using OpenSSL 1.0.1
Security fixes: Upgraded open source libraries with security fixes include WebKit, libpng, OpenSSL, and LibXML. Android 4.2 also includes fixes for Android-specific vulnerabilities. Information about these vulnerabilities has been provided to Open Handset Alliance members and fixes are available in Android Open Source Project. To improve security, some devices with earlier versions of Android may also include these fixes.

Android 1.5

ProPolice to prevent stack buffer overruns (-fstack-protector)
safe_iop to reduce integer overflows
Extensions to OpenBSD dlmalloc to prevent double free() vulnerabilities and to prevent chunk consolidation attacks. Chunk consolidation attacks are a common way to exploit heap corruption.
OpenBSD calloc to prevent integer overflows during memory allocation

Android 2.3

Format string vulnerability protections (-Wformat-security -Werror=format-security)
Hardware-based No eXecute (NX) to prevent code execution on the stack and heap
Linux mmap_min_addr to mitigate null pointer dereference privilege escalation (further enhanced in Android 4.1)

Android 4.0

Address Space Layout Randomization (ASLR) to randomize key locations in memory

Android 4.1

PIE (Position Independent Executable) support
Read-only relocations / immediate binding (-Wl,-z,relro -Wl,-z,now)
dmesg_restrict enabled (avoid leaking kernel addresses)
kptr_restrict enabled (avoid leaking kernel addresses)