CVE-2018-11546 in md4c
Summary
by MITRE
md4c 0.2.5 has a heap-based buffer over-read because md_is_named_entity_contents has an off-by-one error.
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Analysis
by VulDB Data Team • 03/17/2023
The vulnerability identified as CVE-2018-11546 affects the md4c library version 0.2.5, which is a popular markdown parser implementation. This issue represents a heap-based buffer over-read that occurs during the processing of markdown documents containing specific named entities. The flaw exists within the md_is_named_entity_contents function where an off-by-one error allows memory access beyond the allocated buffer boundaries. This type of vulnerability falls under the category of memory safety issues and can potentially lead to unpredictable behavior or system instability when processing malformed input data.
The technical implementation of this vulnerability stems from improper bounds checking within the named entity parsing logic. When the md4c library encounters a named HTML entity within markdown text, it attempts to validate whether the entity contents conform to expected patterns. The off-by-one error in the md_is_named_entity_contents function causes the parser to read one byte beyond the allocated memory buffer, potentially accessing uninitialized or adjacent memory regions. This memory access violation can result in information disclosure, application crashes, or in some scenarios, arbitrary code execution depending on the memory layout and exploitation conditions. The vulnerability is classified as a CWE-125: Out-of-bounds Read, which is a well-documented weakness in software security practices related to improper input validation and memory access controls.
The operational impact of this vulnerability extends beyond simple parsing failures as it affects any application or system that relies on the md4c library for markdown processing. Web applications, documentation generators, content management systems, and any software that accepts user-provided markdown content are potentially at risk. Attackers could exploit this vulnerability by crafting malicious markdown documents containing specially formatted named entities that trigger the buffer over-read condition. The exploitation scenario typically involves an attacker providing malformed markdown input that, when processed by the vulnerable library, causes the application to read beyond allocated memory boundaries. This can lead to denial of service conditions, data corruption, or in more sophisticated attacks, information leakage that could aid further exploitation attempts.
Mitigation strategies for CVE-2018-11546 involve immediate software updates to the md4c library to version 0.2.6 or later, which contains the necessary fixes for the buffer over-read vulnerability. System administrators and developers should conduct thorough vulnerability assessments to identify all applications and services that utilize the affected library. Additionally, input validation measures should be implemented at multiple layers including application-level sanitization and runtime monitoring to detect potential exploitation attempts. The ATT&CK framework categorizes this type of vulnerability under T1210: Exploitation of Remote Services, as it represents a common attack vector through malformed input processing. Organizations should also consider implementing defensive coding practices such as bounds checking, memory safety validations, and regular security audits to prevent similar issues in other components of their software stack. Regular patch management processes should be established to ensure timely updates of third-party libraries and dependencies to address known vulnerabilities.