CVE-2018-11545 in md4c
Summary
by MITRE
md4c 0.2.5 has a heap-based buffer overflow in md_merge_lines because md_is_link_label mishandles the case of a link label composed solely of backslash escapes.
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Analysis
by VulDB Data Team • 03/17/2023
The vulnerability identified as CVE-2018-11545 affects the md4c markdown parsing library version 0.2.5, specifically within the md_merge_lines function where a heap-based buffer overflow occurs. This flaw stems from improper handling of link labels that consist exclusively of backslash escapes, creating a condition where memory corruption can occur during the parsing process. The issue represents a critical security concern as it allows for potential arbitrary code execution when malformed markdown content is processed by applications relying on this library.
The technical root cause of this vulnerability lies in the md_is_link_label function which fails to properly validate or handle edge cases involving backslash-escaped characters in link labels. When the parser encounters a link label composed entirely of backslash escapes, the function does not correctly account for the memory allocation required to process these sequences, leading to a situation where more data is written to a heap buffer than it can accommodate. This memory corruption vulnerability falls under the CWE-121 heap-based buffer overflow category, which is classified as a common weakness in software security practices.
The operational impact of this vulnerability extends beyond simple parsing failures, as it creates a potential attack surface for remote code execution when applications process untrusted markdown input. Attackers could craft malicious markdown documents containing specially formatted link labels with only backslash escapes, causing the md4c library to overflow buffers and potentially overwrite adjacent memory regions. This type of vulnerability aligns with ATT&CK technique T1203, which involves gaining access to systems through the exploitation of software vulnerabilities, and demonstrates how seemingly benign parsing operations can become weaponized attack vectors.
Systems utilizing md4c version 0.2.5 for processing markdown content, particularly those handling user-generated input or external data sources, face significant risk from this vulnerability. The heap overflow could be exploited to execute arbitrary code with the privileges of the affected application, potentially leading to complete system compromise. Organizations should prioritize updating to patched versions of md4c, implementing input validation measures, and monitoring for exploitation attempts. The vulnerability also highlights the importance of proper memory management and input validation in text processing libraries, as these components often serve as foundational elements in applications across multiple security domains.