CVE-2022-24724 in cmark-gfm
Summary
by MITRE • 03/03/2022
cmark-gfm is GitHub's extended version of the C reference implementation of CommonMark. Prior to versions 0.29.0.gfm.3 and 0.28.3.gfm.21, an integer overflow in cmark-gfm's table row parsing `table.c:row_from_string` may lead to heap memory corruption when parsing tables who's marker rows contain more than UINT16_MAX columns. The impact of this heap corruption ranges from Information Leak to Arbitrary Code Execution depending on how and where `cmark-gfm` is used. If `cmark-gfm` is used for rendering remote user controlled markdown, this vulnerability may lead to Remote Code Execution (RCE) in applications employing affected versions of the `cmark-gfm` library. This vulnerability has been patched in the following cmark-gfm versions 0.29.0.gfm.3 and 0.28.3.gfm.21. A workaround is available. The vulnerability exists in the table markdown extensions of cmark-gfm. Disabling the table extension will prevent this vulnerability from being triggered.
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Analysis
by VulDB Data Team • 03/06/2022
The cmark-gfm library represents GitHub's enhanced implementation of the CommonMark markdown specification, widely adopted for parsing and rendering markdown content across various applications and platforms. This particular vulnerability resides within the table parsing functionality of the library, specifically in the `table.c:row_from_string` function that processes table marker rows. The flaw manifests as an integer overflow condition that occurs when parsing table rows containing an excessive number of columns exceeding the UINT16_MAX limit of 65535 columns. This overflow condition creates a critical memory corruption vulnerability that can be exploited across different operational contexts.
The technical implementation of this vulnerability stems from inadequate input validation and overflow protection within the table parsing logic. When the parser encounters a table row with more than 65535 columns, the integer arithmetic fails to properly handle the overflow condition, leading to heap memory corruption. This memory corruption can manifest in multiple ways including information leakage, denial of service, or more critically arbitrary code execution depending on the memory layout and how the vulnerable library is integrated into target applications. The vulnerability operates at the parsing layer where untrusted markdown input is processed, making it particularly dangerous when applications use cmark-gfm to render user-provided content.
The operational impact of CVE-2022-24724 extends beyond simple parsing failures to potentially enable remote code execution in affected applications. When applications employ vulnerable versions of cmark-gfm to process markdown content from untrusted sources, attackers can craft malicious markdown tables that trigger the integer overflow during parsing. This vulnerability aligns with CWE-190, Integer Overflow or Wraparound, which specifically addresses the dangerous consequences of integer arithmetic operations that exceed their representable range. The ATT&CK framework categorizes this as a code injection technique where an attacker can manipulate input processing to achieve arbitrary code execution through memory corruption vulnerabilities. The vulnerability affects any application that processes markdown tables, particularly web applications, content management systems, and any platform that renders user-generated markdown content.
Mitigation strategies for this vulnerability include upgrading to patched versions 0.29.0.gfm.3 or 0.28.3.gfm.21 which contain proper integer overflow protection and bounds checking. The workaround of disabling table extensions provides an effective temporary solution for applications that do not require table functionality, preventing the vulnerable code path from being executed. Security practitioners should prioritize patching affected systems and monitor for any applications that may be using older versions of the library. The vulnerability demonstrates the critical importance of input validation and proper integer handling in parsing libraries, particularly those handling untrusted user input, as these components often serve as attack vectors for more sophisticated exploitation techniques. Organizations should conduct thorough inventory assessments to identify all systems using cmark-gfm and ensure proper version control to prevent exploitation of this and similar vulnerabilities.