CVE-2021-39679 in Android
Summary
by MITRE • 01/14/2022
In init of vendor_graphicbuffer_meta.cpp, there is a possible use after free 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 kernelAndroid ID: A-188745089References: N/A
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Analysis
by VulDB Data Team • 01/19/2022
The vulnerability identified as CVE-2021-39679 resides within the Android kernel's graphic buffer management subsystem, specifically in the vendor_graphicbuffer_meta.cpp implementation. This flaw represents a critical race condition that can result in a use-after-free scenario, fundamentally compromising system security. The vulnerability affects Android kernel versions and is tracked under Android ID A-188745089, highlighting its significance within the mobile operating system ecosystem where kernel-level security is paramount.
The technical implementation flaw stems from improper synchronization mechanisms during the management of graphic buffer metadata structures. When multiple threads or processes attempt to access and modify the same buffer metadata simultaneously, the race condition allows for a scenario where memory allocated to a graphic buffer object is freed while another process or thread still holds references to it. This memory management error creates a situation where subsequent operations on the freed memory location can result in arbitrary code execution or privilege escalation. The vulnerability is classified under CWE-416 as Use After Free, which directly maps to the race condition exploitation path. The flaw exists in the kernel's memory management routines where proper locking mechanisms are insufficient to prevent concurrent access to shared resources.
The operational impact of this vulnerability is severe as it enables local privilege escalation without requiring any additional execution privileges or user interaction. An attacker with local access to an Android device can exploit this race condition to gain elevated privileges, potentially allowing them to execute arbitrary code with kernel-level permissions. This represents a significant threat vector because it requires no user interaction, making it particularly dangerous for mobile environments where devices may be compromised through various attack surfaces. The exploitability is further enhanced by the fact that the vulnerability exists in kernel space, meaning successful exploitation can lead to complete system compromise. According to ATT&CK framework, this vulnerability maps to T1068 (Local Privilege Escalation) and T1059 (Command and Scripting Interpreter) as attackers can leverage the elevated privileges to execute malicious code and maintain persistence.
The mitigation strategies for CVE-2021-39679 should focus on implementing proper synchronization mechanisms within the kernel's graphic buffer management code. This includes adding robust mutex locks or other concurrency control mechanisms to ensure exclusive access to graphic buffer metadata structures during critical operations. System administrators and device manufacturers should prioritize applying security patches that address the race condition by strengthening the memory management routines in vendor_graphicbuffer_meta.cpp. The fix should involve implementing proper reference counting mechanisms and ensuring that buffer metadata objects are not freed until all references are properly released. Additionally, kernel hardening techniques such as stack canaries and memory randomization should be employed to make exploitation more difficult. Regular security audits of kernel components and adherence to secure coding practices are essential to prevent similar vulnerabilities in future implementations. The vulnerability underscores the importance of rigorous testing for race conditions in kernel-level code and proper memory management practices that align with industry standards for secure software development.