CVE-2019-9469 in Android
Summary
by MITRE
In km_compute_shared_hmac of km4.c, there is a possible out of bounds write due to improper input validation. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation. Product: Android Versions: Android kernel Android ID: A-130246677
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Analysis
by VulDB Data Team • 01/07/2020
The vulnerability identified as CVE-2019-9469 represents a critical out-of-bounds write flaw within the Android kernel's keymaster implementation, specifically in the km_compute_shared_hmac function located in km4.c. This issue resides in the cryptographic subsystem responsible for handling shared secret computations and HMAC operations, making it particularly dangerous for privilege escalation attacks. The vulnerability stems from inadequate input validation mechanisms that fail to properly verify the bounds of user-supplied data before processing it within kernel memory space. According to the Android security advisory A-130246677, this flaw affects the Android kernel's keymaster module which is essential for secure cryptographic operations including key generation, storage, and computation. The absence of proper boundary checks allows malicious actors to craft specially formatted inputs that exceed the allocated memory buffer, potentially corrupting adjacent memory regions and compromising system integrity.
The technical exploitation of this vulnerability leverages the kernel's insufficient validation of input parameters during HMAC computation operations, creating a scenario where an attacker can manipulate the function's behavior through carefully constructed inputs. This flaw operates at the kernel level without requiring any user interaction or additional execution privileges, making it particularly concerning for local privilege escalation attacks. The vulnerability's classification as a local privilege escalation issue aligns with CWE-121, which describes heap-based buffer overflow conditions where insufficient validation of input data allows for memory corruption. The attack vector specifically targets the keymaster implementation's handling of shared secrets, where improper bounds checking enables attackers to overwrite adjacent memory locations with controlled data. This type of vulnerability falls under the ATT&CK technique T1068, which involves exploiting legitimate credentials and system privileges to gain elevated access, though in this case the escalation occurs through memory corruption rather than credential theft.
The operational impact of CVE-2019-9469 extends beyond simple privilege escalation as it represents a fundamental weakness in Android's cryptographic security infrastructure. When exploited successfully, this vulnerability allows local attackers to execute arbitrary code with kernel-level privileges, potentially enabling full system compromise and persistent access. The affected Android kernel versions demonstrate the widespread nature of this flaw, as it impacts core cryptographic operations that are critical for device security. The vulnerability's exploitation requires no user interaction, meaning that any local process with access to the keymaster interface could potentially leverage this flaw. Security researchers have noted that the memory corruption pattern associated with this issue can lead to unpredictable system behavior including kernel panics, data corruption, and complete system instability. The lack of user interaction requirements makes this vulnerability particularly dangerous in environments where local access is possible, such as devices with unlocked bootloaders or those running debug builds, where the attack surface is expanded without additional security barriers.
Mitigation strategies for CVE-2019-9469 should focus on immediate patch deployment through Android security updates, as the vulnerability requires kernel-level fixes to address the root cause. Organizations should implement comprehensive monitoring for unauthorized local access attempts and ensure that all Android devices receive timely security patches. The fix typically involves adding proper input validation and bounds checking within the km_compute_shared_hmac function to prevent memory corruption during HMAC computations. Additionally, system administrators should consider implementing additional security controls such as kernel address space layout randomization and stack canaries to make exploitation more difficult. The vulnerability serves as a reminder of the critical importance of input validation in kernel space operations, particularly in cryptographic modules where memory corruption can lead to complete system compromise. Regular security assessments of kernel components and cryptographic implementations should be conducted to identify similar validation flaws that could enable privilege escalation attacks. Organizations should also maintain updated threat intelligence regarding similar vulnerabilities in Android kernel components and ensure their security posture adapts to evolving attack patterns targeting kernel-level security flaws.