CVE-2018-11536 in md4c
Summary
by MITRE
md4c before 0.2.5 has a heap-based buffer overflow because md_split_simple_pairing_mark mishandles splits.
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Analysis
by VulDB Data Team • 03/17/2023
The vulnerability identified as CVE-2018-11536 represents a critical heap-based buffer overflow in the md4c library version 0.2.4 and earlier. This library serves as a markdown parser implementation that processes markdown documents and converts them into structured formats for various applications. The flaw manifests within the md_split_simple_pairing_mark function which is responsible for handling specific markdown syntax elements involving pairing marks such as emphasis or strong text formatting. The buffer overflow occurs when the library processes malformed markdown input that triggers improper memory allocation during the splitting operation of these pairing marks.
The technical implementation of this vulnerability stems from inadequate bounds checking and memory management within the md4c parser's handling of markdown syntax. When the md_split_simple_pairing_mark function encounters certain input patterns, it fails to properly validate the size of memory allocations required for processing the split operations. This leads to writing beyond the allocated heap buffer boundaries, potentially allowing attackers to overwrite adjacent memory regions. The vulnerability specifically affects the library's ability to handle markdown constructs that require splitting operations, particularly when dealing with nested or improperly formatted emphasis markers. The flaw exists in the memory allocation logic where the system calculates required buffer sizes without sufficient validation against actual input constraints.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as heap-based buffer overflows can potentially enable remote code execution under certain conditions. Attackers could craft malicious markdown documents that, when processed by applications using vulnerable versions of md4c, would trigger the overflow condition. This could lead to arbitrary code execution on systems running affected software, particularly in web applications or document processing systems that accept user-provided markdown content. The vulnerability affects any application or system that relies on md4c for markdown parsing, including content management systems, documentation generators, and collaborative platforms that process markdown input. The exploitation potential increases when applications do not properly sanitize or validate markdown input before processing.
Mitigation strategies for CVE-2018-11536 primarily involve upgrading to md4c version 0.2.5 or later, which contains the necessary fixes for the buffer overflow condition. System administrators and developers should conduct thorough vulnerability assessments to identify all applications and services using vulnerable versions of the library. Additional defensive measures include implementing input validation and sanitization for markdown content, deploying memory protection mechanisms such as stack canaries or address space layout randomization, and monitoring for anomalous memory access patterns. The vulnerability aligns with CWE-121 heap-based buffer overflow classification and represents a significant concern for the ATT&CK framework's execution and privilege escalation tactics. Organizations should prioritize patching this vulnerability as part of their regular security maintenance routines to prevent potential exploitation by threat actors who may target markdown processing systems. The fix implemented in version 0.2.5 addresses the root cause by introducing proper bounds checking and memory allocation validation within the md_split_simple_pairing_mark function, ensuring that all buffer operations remain within allocated memory boundaries.