CVE-2021-39639 in Android
Summary
by MITRE • 12/15/2021
In TBD of fvp.c, there is a possible way to glitch CPU behavior due to a missing permission check. This could lead to local escalation of privilege with physical access to device internals with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-198291476References: N/A
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Analysis
by VulDB Data Team • 12/22/2021
The vulnerability identified as CVE-2021-39639 resides within the fvp.c component of the Android kernel, specifically in a function referred to as TBD. This flaw represents a critical security weakness that stems from an inadequate permission validation mechanism, creating a pathway for unauthorized privilege escalation. The vulnerability is particularly concerning because it can be exploited with physical access to device internals, eliminating the need for additional execution privileges or user interaction during the attack process. The missing permission check in the fvp.c file creates a scenario where malicious actors can manipulate CPU behavior through direct hardware access, potentially compromising the entire system security posture. This type of vulnerability falls under the category of kernel-level flaws that can have far-reaching consequences for device integrity and user data protection.
The technical implementation of this vulnerability involves a race condition or access control bypass within the function where the permission verification is absent or insufficient. When a device with physical access is compromised, an attacker can leverage this missing validation to execute code with elevated privileges, effectively bypassing the normal security boundaries that protect the Android kernel from unauthorized modifications. The flaw is particularly dangerous because it operates at the hardware abstraction layer, where direct CPU manipulation can occur without the typical software-based security controls that would normally prevent such behavior. This type of vulnerability is classified as a privilege escalation issue that can be categorized under CWE-284, which deals with improper access control, and more specifically relates to improper privilege management within kernel components. The attack vector requires only physical access to the device, making it particularly concerning for environments where devices may be compromised through theft or unauthorized physical access.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it can enable attackers to gain complete control over device functions and potentially extract sensitive information from the system. With physical access and no additional privileges required, an attacker can manipulate the CPU behavior through the flawed fvp.c implementation, potentially leading to persistent backdoors or complete system compromise. The vulnerability affects Android kernel implementations and can be exploited across various device models that utilize the affected kernel components, creating a widespread security risk. This type of attack aligns with ATT&CK technique T1068, which involves local privilege escalation through kernel exploits, and demonstrates how physical access can be leveraged to bypass traditional network-based security controls. The implications are significant for mobile device security, as this vulnerability can be exploited in scenarios involving lost or stolen devices, where physical access is readily available to potential attackers.
Mitigation strategies for CVE-2021-39639 should focus on implementing comprehensive permission validation mechanisms within the kernel components, particularly in the fvp.c file where the vulnerability originates. Device manufacturers should prioritize updating kernel implementations to include proper access controls and validation checks that prevent unauthorized CPU behavior manipulation. The recommended approach involves patching the affected kernel code to ensure that all functions requiring specific permissions perform adequate validation before executing privileged operations. Additionally, implementing hardware-based security features such as secure boot mechanisms and trusted execution environments can help prevent exploitation of such vulnerabilities even when physical access is available. Regular security audits of kernel components should be conducted to identify and remediate similar permission validation gaps that could create similar attack vectors. Organizations should also consider implementing device management policies that enforce regular security updates and monitor for potential exploitation attempts through physical access scenarios. The vulnerability serves as a reminder of the importance of robust access control mechanisms at all levels of system implementation, particularly within kernel space where the consequences of inadequate validation can be catastrophic for overall system security.