CVE-2020-29562 in C Library
Summary
by MITRE • 12/04/2020
The iconv function in the GNU C Library (aka glibc or libc6) 2.30 to 2.32, when converting UCS4 text containing an irreversible character, fails an assertion in the code path and aborts the program, potentially resulting in a denial of service.
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Analysis
by VulDB Data Team • 06/09/2025
The vulnerability identified as CVE-2020-29562 represents a critical denial of service weakness within the GNU C Library that affects versions 2.30 through 2.32. This issue specifically targets the iconv function which serves as a crucial component for character encoding conversion in Unix-like operating systems and applications that rely on glibc for their core functionality. The flaw manifests when processing UCS4 text containing characters that cannot be converted to the target encoding, triggering an assertion failure that causes program termination. This behavior fundamentally undermines system stability and availability, particularly in environments where applications depend heavily on international character set support and text processing capabilities.
The technical implementation of this vulnerability stems from inadequate error handling within the iconv function's code path responsible for UCS4 character conversions. When encountering irreversible character mappings during the conversion process, the system fails to gracefully handle the condition and instead executes an assertion check that results in immediate program abortion. This assertion failure represents a classic example of improper error handling that violates fundamental security principles and can be exploited by malicious actors to disrupt services. The vulnerability maps to CWE-617, which specifically addresses reachable assertions that can be triggered by external input, and aligns with ATT&CK technique T1499.004 for network denial of service attacks through resource exhaustion or program termination.
The operational impact of this vulnerability extends far beyond simple program crashes, as it can compromise entire application stacks and system services that depend on glibc's iconv functionality. Applications including web servers, database systems, email servers, and network daemons that process user input containing UCS4 encoded text may become unavailable when attackers deliberately feed them malformed character sequences. This vulnerability particularly affects systems handling international text processing, multilingual applications, and any software that performs character encoding conversions as part of normal operation. The denial of service can be achieved with relatively simple input payloads, making it an attractive attack vector for adversaries seeking to disrupt service availability.
Mitigation strategies for CVE-2020-29562 primarily focus on immediate system updates and patch management to upgrade glibc to versions 2.33 or later where the assertion failure has been resolved. Organizations should prioritize patching affected systems, particularly those running web applications, database servers, and any service that processes user-generated text input. Additionally, implementing input validation and sanitization measures can provide defense-in-depth protection by filtering out potentially malicious character sequences before they reach the vulnerable iconv function. System administrators should also consider monitoring for abnormal program termination patterns and implementing process restart mechanisms to maintain service availability. The vulnerability demonstrates the critical importance of proper error handling in system libraries and underscores the need for comprehensive testing of international character set processing capabilities in security-conscious environments.