CVE-2021-31870 in klibc
Summary
by MITRE • 04/30/2021
An issue was discovered in klibc before 2.0.9. Multiplication in the calloc() function may result in an integer overflow and a subsequent heap buffer overflow.
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Analysis
by VulDB Data Team • 05/03/2021
The vulnerability identified as CVE-2021-31870 resides within the klibc library version 2.0.8 and earlier, representing a critical integer overflow condition that can lead to heap buffer overflow. This flaw specifically affects the calloc() function implementation within the kernel library, which is widely used in embedded systems and Linux kernel space applications. The issue manifests when the calloc() function performs multiplication operations to calculate memory allocation sizes, where insufficient input validation allows maliciously crafted parameters to trigger arithmetic overflow conditions.
The technical exploitation of this vulnerability occurs through the calloc() function's handling of memory allocation requests where the multiplication of requested elements and element size exceeds the maximum representable value for the integer type used in the calculation. This overflow results in a smaller calculated size than requested, leading to insufficient memory allocation for the actual data structure. When subsequent operations attempt to write beyond this artificially constrained buffer, heap corruption occurs, potentially allowing attackers to execute arbitrary code or cause denial of service conditions.
From an operational impact perspective, this vulnerability affects systems that rely on klibc for memory management in kernel space operations, particularly embedded devices, IoT systems, and kernel modules that utilize calloc() for dynamic memory allocation. The vulnerability is particularly concerning because it operates at a low-level kernel library that many system components depend upon, making the attack surface extensive across various device types. The integer overflow condition can be triggered through malformed input parameters passed to calloc() calls, which may occur during normal system operation or through crafted malicious inputs.
The vulnerability aligns with CWE-190, Integer Overflow or Wraparound, and CWE-121, Stack-based Buffer Overflow, representing a classic example of how improper integer arithmetic can lead to memory corruption vulnerabilities. From an ATT&CK framework perspective, this vulnerability maps to T1059.001 Command and Scripting Interpreter: PowerShell and T1059.007 Command and Scripting Interpreter: Python, as attackers may leverage such memory corruption flaws to execute arbitrary code, and T1203 Exploitation for Client Execution, since the vulnerability can be exploited to gain unauthorized code execution within the kernel context.
Mitigation strategies for this vulnerability include immediate upgrading to klibc version 2.0.9 or later, where the integer overflow protection has been implemented through proper input validation and size calculation bounds checking. System administrators should also implement runtime monitoring to detect anomalous memory allocation patterns that may indicate exploitation attempts. Additionally, source code reviews should be conducted to identify any custom implementations of calloc() or similar memory allocation functions that may be susceptible to similar issues, and defensive programming techniques such as using safe integer arithmetic libraries should be employed to prevent similar vulnerabilities in future implementations.