CVE-2012-6656 in C Library
Summary
by MITRE
iconvdata/ibm930.c in GNU C Library (aka glibc) before 2.16 allows context-dependent attackers to cause a denial of service (out-of-bounds read) via a multibyte character value of "0xffff" to the iconv function when converting IBM930 encoded data to UTF-8.
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Analysis
by VulDB Data Team • 02/27/2022
The vulnerability identified as CVE-2012-6656 resides within the GNU C Library's iconv function implementation, specifically in the iconvdata/ibm930.c file. This flaw represents a classic out-of-bounds read condition that occurs during multibyte character conversion processes, particularly when transforming IBM930 encoded data into UTF-8 format. The issue manifests when the iconv function encounters a multibyte character value of 0xffff during the conversion process, creating a scenario where the library attempts to access memory beyond the allocated buffer boundaries. Such out-of-bounds memory access represents a fundamental violation of memory safety principles and constitutes a significant security concern within the system's foundational libraries.
The technical implementation of this vulnerability stems from inadequate input validation within the IBM930 character set conversion logic. When processing multibyte sequences, the glibc iconv function fails to properly validate the range of character values being processed, allowing malicious inputs containing the specific value 0xffff to bypass normal boundary checks. This particular value represents a problematic edge case in the IBM930 encoding scheme that, when processed through the iconv conversion pipeline, triggers an internal buffer overflow condition. The vulnerability operates at the intersection of character encoding standards and memory management, where the conversion routine does not properly account for all valid character ranges within the source encoding, leading to unauthorized memory access patterns that can be exploited by context-dependent attackers.
From an operational impact perspective, this vulnerability enables attackers to cause denial of service conditions across systems utilizing affected glibc versions. The out-of-bounds read condition can result in application crashes, system instability, or complete service disruption when legitimate applications process data containing the malicious character sequence. This vulnerability is particularly concerning because it affects a core system library that numerous applications depend upon, potentially creating cascading effects throughout the system infrastructure. The context-dependent nature of the attack means that exploitation requires specific conditions where the vulnerable iconv function is invoked with IBM930 encoded data containing the 0xffff character, making it difficult to exploit in automated attacks but still a significant risk for targeted operations. The vulnerability aligns with CWE-129, which addresses improper validation of the length of input data, and represents a clear violation of the principle of least privilege in memory access operations.
The mitigation strategies for CVE-2012-6656 primarily focus on upgrading to patched versions of glibc, specifically versions 2.16 and later where the vulnerability has been addressed through enhanced input validation and proper boundary checking. System administrators should prioritize patching affected systems, particularly those handling multibyte character data or applications that rely heavily on iconv functionality for text processing. Additional defensive measures include implementing input sanitization routines that validate character ranges before processing through iconv functions, monitoring for unusual memory access patterns, and conducting regular vulnerability assessments of system libraries. Organizations should also consider implementing network segmentation and access controls to limit potential attack vectors that could leverage this vulnerability. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service tactics, as it can be leveraged to disrupt system services and potentially create opportunities for further exploitation. Regular security updates and patch management processes become critical in preventing exploitation of such foundational library vulnerabilities that can affect entire application ecosystems.