CVE-2021-39682 in Android
Summary
by MITRE • 01/14/2022
In mgm_alloc_page of memory_group_manager.c, there is a possible out of bounds write due to an incorrect bounds check. 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-201677538References: N/A
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Analysis
by VulDB Data Team • 01/19/2022
The vulnerability identified as CVE-2021-39682 resides within the Android kernel's memory management subsystem, specifically in the memory_group_manager.c source file where the mgm_alloc_page function exhibits a critical out-of-bounds write flaw. This issue stems from an incorrect bounds check implementation that fails to properly validate memory allocation parameters, creating a scenario where malicious code could potentially overwrite adjacent memory regions. The vulnerability is classified under CWE-787, which represents out-of-bounds write conditions that occur when a program writes data past the end of a buffer or array, making it a direct threat to system stability and security.
The technical flaw manifests when the memory_group_manager component processes page allocation requests, where the bounds checking logic fails to account for all possible memory boundaries during allocation operations. This incorrect validation allows an attacker to manipulate the allocation parameters in such a way that subsequent memory writes extend beyond intended buffer limits. The vulnerability operates at the kernel level, meaning that exploitation does not require additional privileges beyond what is normally available to a user-space process, as the flaw exists within the core memory management functionality that handles all allocation requests regardless of user context.
The operational impact of this vulnerability extends to potential local privilege escalation, allowing an attacker with minimal privileges to elevate their access level within the system. This represents a significant security risk because it bypasses normal privilege boundaries that typically protect kernel-level resources from unauthorized access. The exploitation process requires no user interaction, making it particularly dangerous as it can be triggered automatically when the affected kernel component processes memory allocation requests. This characteristic aligns with ATT&CK technique T1068, which involves the exploitation of local privilege escalation vulnerabilities to gain higher system privileges.
The vulnerability's presence in the Android kernel creates widespread exposure across all Android devices that utilize affected kernel versions, particularly those running Android versions prior to the patch release that addressed this specific flaw. The memory_group_manager component is fundamental to Android's memory management architecture, making this vulnerability particularly impactful as it affects core system functionality that all applications and system services depend upon. The lack of user interaction requirements means that exploitation can occur silently in the background without any visible indication to the end user, potentially allowing attackers to establish persistent access to the device.
Mitigation strategies for this vulnerability should focus on immediate kernel updates that contain the patched memory_group_manager.c implementation with corrected bounds checking logic. Organizations and device manufacturers must prioritize deployment of security patches that address the specific bounds validation error in the mgm_alloc_page function. Additionally, system administrators should monitor for any signs of exploitation attempts and implement enhanced memory monitoring capabilities to detect anomalous allocation patterns that might indicate exploitation attempts. The fix should ensure that all buffer boundaries are properly validated before any write operations occur, implementing robust bounds checking that accounts for all potential edge cases in memory allocation scenarios.