CVE-2021-39649 in Android
Summary
by MITRE • 12/15/2021
In regmap_exit of regmap.c, there is a possible use-after-free due to improper locking. This could lead to local escalation of privilege in the kernel with System execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-174049006References: N/A
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Analysis
by VulDB Data Team • 12/18/2021
The vulnerability identified as CVE-2021-39649 represents a critical use-after-free condition within the Linux kernel's regmap subsystem, specifically in the regmap_exit function of regmap.c. This flaw exists within the Android kernel ecosystem and demonstrates a fundamental issue with memory management and synchronization mechanisms. The regmap subsystem serves as a crucial interface for managing register maps in various hardware components, making this vulnerability particularly dangerous as it affects core kernel functionality that underpins device operation and hardware abstraction layers.
The technical root cause stems from improper locking mechanisms during the cleanup process of register map structures. When the regmap_exit function executes, it fails to properly synchronize access to shared resources, creating a window where freed memory can be accessed by concurrent threads or processes. This race condition allows for memory corruption that can be exploited to execute arbitrary code with kernel privileges. The vulnerability manifests as a classic use-after-free scenario where the kernel attempts to access memory that has already been deallocated, potentially leading to memory corruption and privilege escalation.
The operational impact of this vulnerability extends beyond simple memory corruption, as it enables local privilege escalation to kernel level execution privileges without requiring user interaction or additional attack vectors. An attacker with local access to an Android device can leverage this flaw to gain system-level control, potentially compromising the entire device. The attack vector is particularly concerning because it operates entirely within the kernel space, bypassing traditional user-space security mechanisms and protections. This vulnerability affects Android kernel versions and represents a significant threat to device security and integrity.
Mitigation strategies for CVE-2021-39649 should focus on implementing proper locking mechanisms within the regmap_exit function to prevent concurrent access to freed memory structures. System administrators and device manufacturers should prioritize applying kernel updates that address this specific race condition in the regmap subsystem. The fix typically involves ensuring that proper mutex or spinlock mechanisms are employed during the cleanup process to prevent other threads from accessing the register map structure after it has been freed. Additionally, comprehensive testing of kernel memory management and synchronization primitives should be conducted to identify similar race conditions in other subsystems. This vulnerability aligns with CWE-416 which addresses use-after-free conditions and demonstrates the importance of proper resource management in kernel space operations. The ATT&CK framework categorizes this as a privilege escalation technique, specifically targeting kernel-level vulnerabilities that can be exploited for system compromise.