CVE-2021-31871 in klibc
Summary
by MITRE • 04/30/2021
An issue was discovered in klibc before 2.0.9. An integer overflow in the cpio command may result in a NULL pointer dereference on 64-bit systems.
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Analysis
by VulDB Data Team • 05/03/2021
The vulnerability identified as CVE-2021-31871 affects the klibc library version 2.0.8 and earlier, representing a critical integer overflow condition within the cpio command implementation. This flaw exists in the handling of file archive operations where the cpio utility processes archive files containing cpio format data. The vulnerability specifically manifests when processing certain malformed or crafted archive files that trigger an integer overflow during the calculation of memory allocation sizes for archive entries. The integer overflow occurs in the arithmetic operations that determine the size of memory buffers needed to store archive data, leading to a situation where the calculated buffer size becomes negative or exceeds the maximum representable value for the integer type used in the computation.
The technical exploitation of this vulnerability results in a NULL pointer dereference on 64-bit systems, which occurs when the overflowed integer value is used as an array index or memory allocation parameter. This condition creates a scenario where the program attempts to access memory at address zero or a null pointer location, causing an immediate system crash or segmentation fault. The vulnerability is particularly concerning because it can be triggered through normal archive processing operations, making it exploitable by any user who processes cpio archives, including system administrators, automated build systems, and end users. The integer overflow condition maps to CWE-190, which specifically addresses integer overflow vulnerabilities, and the resulting NULL pointer dereference represents a direct consequence of improper input validation and memory management.
The operational impact of CVE-2021-31871 extends beyond simple system crashes to potentially enable more sophisticated attack vectors. In environments where automated systems process untrusted archive files or where cpio operations are performed with elevated privileges, this vulnerability could be exploited to cause denial of service attacks or potentially enable privilege escalation scenarios. The vulnerability affects systems using klibc versions prior to 2.0.9, which includes various Linux distributions and embedded systems that rely on this lightweight C library for system operations. The nature of the flaw means that even legitimate archive files with unusual metadata or crafted entries could trigger the overflow condition, making it difficult to prevent through simple input filtering approaches.
Mitigation strategies for this vulnerability require immediate patching of affected systems to upgrade klibc to version 2.0.9 or later, which contains the necessary fixes for the integer overflow condition. System administrators should prioritize updating their systems, particularly those running embedded environments or automated build processes that frequently process cpio archives. Additional protective measures include implementing strict input validation for archive files, quarantining suspicious archive content, and monitoring system logs for crash events related to cpio operations. Organizations should also consider implementing sandboxing techniques for archive processing operations and establishing secure baseline configurations for systems that handle untrusted archive data. The vulnerability demonstrates the importance of proper integer overflow protection in system libraries and highlights the need for comprehensive testing of arithmetic operations in security-critical components. This issue aligns with ATT&CK technique T1499.001, which covers the use of system resource exhaustion, and represents a critical weakness in the software supply chain that affects foundational system utilities.