CVE-2021-0955 in Android
Summary
by MITRE • 12/15/2021
In pf_write_buf of FuseDaemon.cpp, there is possible memory corruption due to a race condition. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android-11Android ID: A-192085766
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Analysis
by VulDB Data Team • 12/22/2021
The vulnerability identified as CVE-2021-0955 resides within the FuseDaemon.cpp component of Android systems, specifically in the pf_write_buf function where a race condition exists that can result in memory corruption. This flaw represents a critical security issue that allows for local privilege escalation without requiring any additional execution privileges or user interaction for exploitation. The vulnerability affects Android 11 systems and is tracked under Android ID A-192085766, indicating its severity and the need for immediate attention from device manufacturers and security professionals.
The technical root cause of this vulnerability stems from improper synchronization mechanisms within the Fuse daemon implementation, which handles file system operations for Android's FUSE (Filesystem in Userspace) functionality. When multiple threads attempt to write to the buffer simultaneously without proper locking mechanisms, the race condition creates an opportunity for memory corruption to occur. This memory corruption can be exploited to overwrite critical memory locations, potentially allowing an attacker to manipulate the execution flow of the daemon process and elevate their privileges to the system level. The flaw falls under CWE-362, which specifically addresses race conditions, and aligns with ATT&CK technique T1068, which covers local privilege escalation through race conditions.
The operational impact of this vulnerability is significant as it provides a pathway for local attackers to gain elevated system privileges without requiring any special permissions or user interaction. This means that any application or process running with standard user privileges could potentially exploit this flaw to achieve root access. The lack of user interaction requirement makes this vulnerability particularly dangerous as it can be exploited automatically without the need for social engineering or other attack vectors. The memory corruption aspect allows for arbitrary code execution within the privileged context of the Fuse daemon, potentially enabling full system compromise. Organizations deploying Android 11 systems should consider this vulnerability as a high-priority issue requiring immediate remediation.
Mitigation strategies for CVE-2021-0955 should focus on implementing proper synchronization mechanisms within the Fuse daemon's buffer handling code. The most effective approach involves adding appropriate mutex locks or other thread synchronization primitives to prevent concurrent access to the pf_write_buf function. Device manufacturers should prioritize applying the latest security patches provided by Google, which typically include fixes for race conditions in system-level components. Additionally, security teams should monitor for any unauthorized access attempts to the Fuse daemon and implement runtime protections such as stack canaries or address space layout randomization to make exploitation more difficult. The fix should be validated through comprehensive testing to ensure that the synchronization mechanisms do not introduce performance degradation or other unintended side effects in the file system operations.