CVE-2014-6040 in C Library
Summary
by MITRE
GNU C Library (aka glibc) before 2.20 allows context-dependent attackers to cause a denial of service (out-of-bounds read and crash) via a multibyte character value of "0xffff" to the iconv function when converting (1) IBM933, (2) IBM935, (3) IBM937, (4) IBM939, or (5) IBM1364 encoded data to UTF-8.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 04/07/2022
The vulnerability identified as CVE-2014-6040 represents a critical out-of-bounds read condition within the GNU C Library's iconv function implementation. This flaw affects glibc versions prior to 2.20 and specifically impacts the conversion of multibyte character encodings to UTF-8 format. The vulnerability manifests when processing IBM933, IBM935, IBM937, IBM939, or IBM1364 encoded data through the iconv function, creating a scenario where an attacker can manipulate input data to trigger memory access violations.
The technical root cause of this vulnerability lies in improper bounds checking within the iconv function's handling of multibyte character sequences. When the iconv function encounters a multibyte character value of 0xffff during conversion from the specified IBM encodings to UTF-8, it fails to validate the input boundaries properly. This results in the function attempting to read memory locations beyond the allocated buffer boundaries, leading to undefined behavior that can manifest as memory corruption or application crashes. The vulnerability operates under CWE-125, which specifically addresses out-of-bounds read conditions in software implementations.
From an operational perspective, this vulnerability presents significant security implications for systems relying on glibc for character encoding conversions. Attackers can exploit this flaw to cause denial of service conditions across applications that utilize the iconv function for text processing, potentially affecting web servers, database systems, and other software components that perform character encoding transformations. The impact extends beyond simple service disruption as the out-of-bounds read could potentially be leveraged for more sophisticated attacks if combined with other vulnerabilities, though the primary risk remains denial of service.
The attack vector requires context-dependent conditions where an attacker can control input data that flows through the iconv function. This makes the vulnerability particularly concerning in web applications and services that process user-supplied text data, as attackers can craft malicious input sequences containing the specific 0xffff multibyte value to trigger the vulnerability. The exploitation process involves preparing specially crafted IBM-encoded data that, when processed by iconv, causes the memory access violation.
System administrators and security professionals should prioritize patching affected systems with glibc version 2.20 or later, which contains the necessary fixes for this vulnerability. Additionally, implementing input validation measures that sanitize character encoding data before processing can provide defense-in-depth protection. Monitoring for unusual application crashes or memory access patterns during text processing operations can help detect exploitation attempts. The vulnerability also highlights the importance of regular security updates and maintaining current versions of core system libraries, as this issue affects a fundamental component of most unix-like operating systems and their applications. Organizations should also consider implementing application-level restrictions on character encoding conversions and monitoring for suspicious input patterns that could indicate exploitation attempts.