CVE-2021-39733 in Android
Summary
by MITRE • 03/16/2022
In amcs_cdev_unlocked_ioctl of audiometrics.c, there is a possible out of bounds write due to improper input validation. 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-206128522References: N/A
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Analysis
by VulDB Data Team • 03/19/2022
The vulnerability identified as CVE-2021-39733 resides within the Android kernel's audiometrics.c driver component, specifically in the amcs_cdev_unlocked_ioctl function. This represents a critical security flaw that demonstrates poor input validation practices leading to potential privilege escalation. The issue manifests as an out-of-bounds write condition that can be exploited by malicious actors to gain elevated system privileges, requiring only system execution privileges for successful exploitation. The vulnerability's classification as a local privilege escalation vector indicates that an attacker must already have some level of system access but can leverage this flaw to move from their current privilege level to a higher administrative position.
The technical implementation of this vulnerability stems from inadequate bounds checking within the ioctl handling mechanism of the audiometrics character device driver. When processing user-supplied ioctl commands, the function fails to properly validate input parameters before performing memory operations. This allows an attacker to craft malicious ioctl requests that can overwrite memory locations beyond the intended buffer boundaries. The flaw specifically affects the Android kernel's audio metrics subsystem, which is responsible for collecting and managing audio-related performance data. The improper input validation creates a scenario where attacker-controlled data can be used to manipulate kernel memory structures, potentially leading to arbitrary code execution or system compromise.
From an operational perspective, this vulnerability presents significant risk to Android devices since it enables local privilege escalation without requiring user interaction. The attack vector is particularly concerning because it can be exploited by applications running with standard user privileges to gain root access to the underlying system. This capability undermines the fundamental security model of Android systems where applications are typically sandboxed and restricted from accessing privileged system resources. The exploitation of this vulnerability could result in complete system compromise, allowing attackers to modify system files, install malicious applications, or extract sensitive data from the device.
Security professionals should recognize this vulnerability as a variant of CWE-121, which describes stack-based buffer overflow conditions, and potentially related to CWE-787, describing out-of-bounds write conditions. The vulnerability's exploitation aligns with techniques described in the MITRE ATT&CK framework under the privilege escalation tactics, specifically targeting the 'Local Privilege Escalation' and 'Execution' phases. The absence of user interaction requirements makes this vulnerability particularly dangerous as it can be exploited automatically by malware or malicious applications without requiring any form of social engineering or user deception. Organizations should prioritize patching this vulnerability immediately, as the Android kernel updates containing fixes are available through standard security update channels, and the potential impact of exploitation extends beyond individual device compromise to possible large-scale security breaches in environments with multiple Android devices.
The remediation approach for this vulnerability focuses on implementing proper input validation within the amcs_cdev_unlocked_ioctl function to ensure that all user-supplied parameters are thoroughly checked before any memory operations occur. This includes bounds checking on all buffer accesses, proper validation of ioctl command parameters, and implementing defensive programming practices to prevent out-of-bounds memory operations. System administrators should deploy the latest Android kernel security patches and maintain regular update schedules to protect against similar vulnerabilities. The vulnerability also highlights the importance of security code reviews and static analysis tools in identifying potential buffer overflow and memory corruption issues within kernel drivers, emphasizing the need for comprehensive security testing of system-level components that handle user input.