CVE-2018-11547 in md4c
Summary
by MITRE
md_is_link_reference_definition_helper in md4c 0.2.5 has a heap-based buffer over-read because md_is_link_label mishandles loop termination.
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Analysis
by VulDB Data Team • 03/17/2023
The vulnerability identified as CVE-2018-11547 resides within the md4c library version 0.2.5, specifically within the md_is_link_reference_definition_helper function. This issue manifests as a heap-based buffer over-read that occurs due to improper handling of loop termination within the md_is_link_label function. The md4c library serves as a markdown parser implementation that processes markdown documents and converts them into structured output formats. When processing certain malformed or crafted markdown input sequences, the library fails to properly terminate loops that traverse link reference definitions, leading to memory access beyond allocated buffer boundaries.
The technical flaw stems from a classic buffer over-read condition where memory is accessed beyond its allocated limits. The md_is_link_label function, which is responsible for identifying link labels within markdown documents, contains a loop that does not properly check boundary conditions during iteration. This flaw allows attackers to craft malicious markdown content that causes the parser to read memory locations beyond the intended buffer limits, potentially exposing sensitive data or enabling further exploitation. The vulnerability specifically affects the helper function that processes link reference definitions, where the improper loop termination leads to unauthorized memory access patterns.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can potentially be exploited to disclose sensitive information from the application's memory space. Attackers could craft markdown documents that trigger the buffer over-read condition, potentially accessing neighboring memory regions that may contain credentials, session tokens, or other confidential data. This type of vulnerability represents a significant security risk for applications that process untrusted markdown input, such as content management systems, documentation generators, or any platform that renders markdown content from user submissions. The heap-based nature of the over-read means that the vulnerability could be leveraged for information disclosure or potentially contribute to more severe exploitation techniques.
Mitigation strategies for CVE-2018-11547 involve immediate patching of the md4c library to version 0.2.6 or later, which contains the necessary fixes for the loop termination logic. Organizations should also implement input validation and sanitization measures to reduce the attack surface when processing markdown content. Additionally, runtime protections such as address space layout randomization and stack canaries can provide additional defense-in-depth measures. This vulnerability aligns with CWE-125: Out-of-bounds Read, which is categorized under the broader class of buffer overflow vulnerabilities. From an ATT&CK framework perspective, this represents a potential information disclosure technique that could be used to extract sensitive data from memory, potentially enabling further attacks within the compromised system. The vulnerability demonstrates the critical importance of proper loop boundary checking in security-sensitive code and highlights the need for thorough input validation in parsing libraries that handle untrusted data.