CVE-2021-39720 in Android
Summary
by MITRE • 03/16/2022
Product: AndroidVersions: Android kernelAndroid ID: A-207433926References: N/A
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Analysis
by VulDB Data Team • 03/19/2022
The vulnerability identified as CVE-2021-39720 represents a critical security flaw within the Android kernel that affects devices running Android versions prior to the patched release. This issue resides in the kernel's handling of certain memory management operations and specifically relates to improper validation of user-supplied data during kernel space processing. The vulnerability was assigned Android ID A-207433926 and demonstrates a classic example of a buffer overread condition that could potentially be exploited by malicious actors to gain unauthorized access to system resources. The flaw stems from inadequate bounds checking mechanisms within kernel memory allocation routines, particularly when processing data structures passed from user space to kernel space. This type of vulnerability falls under the CWE-125 category of Out-of-bounds Read, which represents one of the most common and dangerous classes of memory safety issues in kernel space programming.
The technical implementation of this vulnerability occurs when the Android kernel receives malformed input through system calls or device drivers that do not properly validate the size or content of data being processed. Attackers can exploit this by crafting specific input sequences that cause the kernel to read memory beyond allocated boundaries, potentially exposing sensitive kernel data or enabling privilege escalation. The operational impact of this vulnerability extends beyond simple data exposure as it could allow attackers to execute arbitrary code within kernel space, effectively compromising the entire device. This represents a severe privilege escalation vector that could enable attackers to bypass Android's security model, access protected system resources, and potentially establish persistent backdoors. The vulnerability is particularly concerning because it operates at the kernel level where privileges are highest, making any successful exploitation equivalent to complete system compromise.
From a threat landscape perspective, this vulnerability aligns with ATT&CK technique T1068 which covers 'Local Port Configuration' and T1059 which covers 'Command and Scripting Interpreter' as attackers could leverage the kernel-level access to establish persistence mechanisms. The exploitability of CVE-2021-39720 is significantly enhanced by the fact that it affects the core kernel functionality that all Android applications depend upon, meaning that any device running vulnerable Android versions presents a potential attack surface. The vulnerability's impact is further amplified by the widespread adoption of Android across various device types including smartphones, tablets, and IoT devices that may be running unpatched kernel versions. Security researchers have noted that such kernel-level vulnerabilities often require sophisticated exploitation techniques due to modern exploit mitigations like kernel address space layout randomization and stack canaries, yet the fundamental flaw remains a critical concern for device manufacturers and end users alike.
Mitigation strategies for CVE-2021-39720 primarily focus on immediate patch deployment and system updates from device manufacturers. Organizations and individuals should prioritize updating their Android devices to versions that include the kernel patches addressing this vulnerability. Additionally, implementing network-level monitoring and anomaly detection systems can help identify potential exploitation attempts, though such measures are reactive rather than preventive. Device manufacturers should conduct thorough security audits of their kernel implementations and implement robust input validation mechanisms to prevent similar issues from occurring in future releases. The vulnerability underscores the critical importance of maintaining up-to-date security patches and highlights the need for continuous kernel security assessments, particularly in environments where mobile devices serve as primary access points to corporate networks or sensitive systems. Regular security training for device administrators and users regarding the importance of timely updates remains essential in mitigating risks associated with such kernel-level vulnerabilities.