CVE-2021-39741 in Android
Summary
by MITRE • 03/30/2022
In Keymaster, there is a possible out of bounds write due to a missing 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-12LAndroid ID: A-173567719
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Analysis
by VulDB Data Team • 04/02/2022
The vulnerability identified as CVE-2021-39741 resides within the Keymaster subsystem of Android operating systems, specifically affecting Android 12L versions. This issue represents a critical security flaw that could enable malicious actors to escalate their privileges from a standard user account to system-level execution privileges without requiring any user interaction. The vulnerability manifests as an out-of-bounds write condition that occurs due to the absence of proper bounds checking mechanisms within the Keymaster implementation. Keymaster serves as a crucial cryptographic service component in Android, responsible for secure key storage and cryptographic operations that form the foundation of device security and encryption capabilities.
The technical nature of this vulnerability places it squarely within the CWE-129 category of Improper Input Validation, specifically manifesting as an out-of-bounds write that occurs when the system fails to validate array indices or buffer limits before performing write operations. This flaw allows an attacker to potentially overwrite memory regions beyond the intended boundaries, creating opportunities for arbitrary code execution and privilege escalation. The vulnerability's classification aligns with ATT&CK technique T1068 which covers Local Privilege Escalation through system-level exploitation. The missing bounds check indicates a fundamental flaw in the input validation process where the Keymaster service does not properly verify that data being written to memory locations remains within allocated buffer boundaries, creating a predictable memory corruption scenario.
The operational impact of this vulnerability is severe as it provides a pathway for local privilege escalation without requiring user interaction, making it particularly dangerous in environments where untrusted applications or users might have access to the device. An attacker could leverage this vulnerability to gain system-level execution privileges, potentially enabling them to access sensitive cryptographic keys, modify system files, or establish persistent backdoors within the device. The exploitation of this vulnerability would allow attackers to bypass Android's security model and gain control over critical cryptographic operations that protect user data and device integrity. This represents a significant threat to device security since the Keymaster service handles sensitive cryptographic operations that are fundamental to Android's security architecture, including secure key storage and hardware-backed encryption mechanisms.
Mitigation strategies for this vulnerability should focus on immediate patch deployment through official Android security updates, which would include the necessary bounds checking mechanisms to prevent the out-of-bounds write condition. Organizations should also implement monitoring for suspicious system-level activities and ensure that all devices are running the latest security patches. Additionally, system administrators should consider implementing additional security controls such as application sandboxing and privilege separation to limit the potential impact of exploitation. The vulnerability highlights the importance of robust input validation and bounds checking in security-critical components, emphasizing that cryptographic services must maintain strict memory boundaries to prevent exploitation. Regular security assessments of cryptographic subsystems and adherence to secure coding practices should be maintained to prevent similar issues in future implementations, particularly focusing on the principles outlined in the OWASP Secure Coding Practices and NIST guidelines for secure software development.