CVE-2021-39731 in Android
Summary
by MITRE • 03/16/2022
In ProtocolStkProactiveCommandAdapter::Init of protocolstkadapter.cpp, there is a possible out of bounds write due to an incorrect bounds check. This could lead to local escalation of privilege with System execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-205036834References: N/A
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Analysis
by VulDB Data Team • 03/19/2022
The vulnerability identified as CVE-2021-39731 represents a critical out-of-bounds write flaw within the Android kernel's ProtocolStkProactiveCommandAdapter component. This issue manifests in the Init function of protocolstkadapter.cpp where an improper bounds check allows for memory corruption that can be exploited to achieve local privilege escalation. The vulnerability specifically affects Android kernel versions and is tracked under Android ID A-205036834, indicating its severity and the need for immediate attention in the Android security ecosystem.
The technical root cause of this vulnerability stems from inadequate input validation within the proactive command adapter mechanism that handles SIM card proactive commands. When processing certain command sequences, the system fails to properly verify array bounds before writing data to memory locations, creating a scenario where malicious input can overwrite adjacent memory regions. This flaw falls under the CWE-787 weakness category, which specifically addresses out-of-bounds write vulnerabilities that can lead to arbitrary code execution and privilege escalation. The vulnerability requires System execution privileges to be exploited, meaning an attacker must already have some level of access to the system before leveraging this flaw to gain elevated privileges.
The operational impact of CVE-2021-39731 extends beyond simple memory corruption as it enables local privilege escalation to system-level privileges, potentially allowing attackers to execute arbitrary code with the highest possible system permissions. This type of vulnerability is particularly dangerous in mobile environments where the kernel represents the core security boundary between user applications and system-level operations. The exploitation of this flaw could result in complete system compromise, enabling attackers to access sensitive user data, modify system configurations, or establish persistent backdoors. The vulnerability's classification as requiring only local execution privileges makes it especially concerning since it can be exploited by malicious applications already present on the device.
Mitigation strategies for this vulnerability should focus on immediate patch deployment through Android security updates, as the flaw exists within core kernel components that require system-level fixes. Organizations should implement comprehensive monitoring for suspicious process behaviors and memory access patterns that could indicate exploitation attempts. The ATT&CK framework's T1068 technique for "Exploitation for Privilege Escalation" and T1059 for "Command and Scripting Interpreter" should be considered when developing defensive measures, as attackers may attempt to leverage this vulnerability to establish persistent access. Additionally, implementing kernel address space layout randomization and other exploit mitigations can help reduce the effectiveness of potential exploitation attempts, though the most effective solution remains timely patching of the affected Android kernel components to prevent unauthorized privilege escalation.