CVE-2021-39634 in Android
Summary
by MITRE • 01/14/2022
In fs/eventpoll.c, there is a possible use after free. 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-204450605References: Upstream kernel
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Analysis
by VulDB Data Team • 01/19/2022
The vulnerability identified as CVE-2021-39634 resides within the Linux kernel's eventpoll subsystem, specifically in the fs/eventpoll.c file where a use-after-free condition has been discovered. This critical flaw represents a memory safety issue that can be exploited to achieve local privilege escalation without requiring any special execution privileges or user interaction for exploitation. The vulnerability affects Android kernel implementations and has been assigned the Android ID A-204450605 by the Android security team. The upstream kernel reference indicates this issue has been documented and addressed in the mainline kernel development stream, making it a well-known and documented security gap that impacts the fundamental operating system kernel functionality.
The technical flaw manifests as a use-after-free vulnerability that occurs when the eventpoll subsystem handles file descriptor operations in the kernel space. This particular weakness allows an attacker to manipulate memory structures that have already been freed, potentially leading to arbitrary code execution or privilege escalation. The memory management error occurs during the processing of epoll events, where improper handling of file descriptor cleanup creates opportunities for malicious code to exploit the freed memory locations. This type of vulnerability falls under the Common Weakness Enumeration category CWE-416, which specifically addresses Use After Free conditions in software development, making it a well-documented and understood class of memory safety issues within the cybersecurity community.
The operational impact of this vulnerability is severe for Android devices since it enables local privilege escalation without requiring any user interaction or elevated privileges. An attacker with local access to an Android device can leverage this flaw to gain root-level privileges, effectively compromising the entire system security model. The exploitation process does not require any special user input or interaction, making it particularly dangerous as it can be triggered automatically. This vulnerability essentially undermines the kernel's memory safety mechanisms and can potentially allow attackers to execute malicious code with the highest system privileges, rendering the device completely compromised. The lack of user interaction requirement means this vulnerability can be exploited in automated attacks or during normal device operation, making it a persistent threat to Android device security.
Mitigation strategies for CVE-2021-39634 primarily involve applying the upstream kernel patches that address the specific memory management issues in the eventpoll subsystem. Android device manufacturers should implement the latest kernel security updates and ensure that devices receive timely security patches to protect against this vulnerability. System administrators and security teams should prioritize patch deployment across all affected Android devices, particularly those in enterprise environments where device security is paramount. The vulnerability's classification under ATT&CK technique T1068, which covers Exploitation for Privilege Escalation, indicates that organizations should monitor for potential exploitation attempts and implement appropriate network detection measures. Additionally, organizations should consider implementing memory safety monitoring tools and regular security assessments to identify potential exploitation attempts targeting this specific kernel vulnerability.