CVE-2021-39683 in Android
Summary
by MITRE • 01/14/2022
In copy_from_mbox of sss_ice_util.c, 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 kernelAndroid ID: A-202003354References: N/A
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Analysis
by VulDB Data Team • 01/19/2022
The vulnerability identified as CVE-2021-39683 represents a critical out-of-bounds write flaw within the Android kernel's sss_ice_util.c component specifically in the copy_from_mbox function. This issue stems from the absence of proper bounds checking mechanisms that should validate the size of data being copied from a mailbox buffer to a destination buffer. The flaw exists at the kernel level, making it particularly dangerous as it operates within the privileged system execution context where such vulnerabilities can be exploited to gain elevated privileges.
The technical implementation of this vulnerability manifests in the copy_from_mbox function where data transfer occurs without adequate validation of buffer boundaries. When the function processes data from a mailbox structure, it fails to verify that the source data length does not exceed the allocated buffer size in the destination memory region. This missing bounds check creates an opportunity for attackers to write data beyond the intended memory boundaries, potentially corrupting adjacent memory locations or overwriting critical kernel data structures. The vulnerability falls under the CWE-129 weakness category, which specifically addresses insufficient boundary checking, and aligns with the ATT&CK technique T1068, which covers 'Local Privilege Escalation' through kernel exploits.
The operational impact of this vulnerability extends beyond simple memory corruption as it enables local privilege escalation with system execution privileges required for exploitation. While user interaction is not necessary for exploitation, the requirement for system execution privileges means that an attacker must first compromise a system to reach the kernel level. This makes the vulnerability particularly concerning in environments where local access is possible, such as in mobile devices or embedded systems where physical access or initial compromise could lead to complete system control. The nature of kernel-level vulnerabilities means that successful exploitation could result in complete system compromise, allowing attackers to execute arbitrary code with the highest privileges available.
Mitigation strategies for CVE-2021-39683 should focus on implementing proper bounds checking mechanisms within the copy_from_mbox function and related mailbox handling code. The most effective approach involves adding comprehensive validation checks that verify source data size against destination buffer capacity before any memory copying operations occur. Android security patches would typically address this by modifying the sss_ice_util.c file to include proper boundary validation logic, ensuring that data transfer operations respect allocated buffer limits. Organizations should prioritize applying the latest security updates from Google and device manufacturers, as these patches will contain the necessary code modifications to prevent the out-of-bounds write condition. Additionally, system administrators should consider implementing runtime protections such as stack canaries, address space layout randomization, and kernel memory protection mechanisms to reduce the effectiveness of potential exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation in kernel code and highlights why security reviews of system-level components must include thorough examination of memory management operations and buffer handling procedures.