Quadratic complexity may lead to a denial of service in cmark-gfm

Summary

cmark-gfm is GitHub's fork of cmark, a CommonMark parsing and rendering library and program in C. A polynomial time complexity issue in cmark-gfm may lead to unbounded resource exhaustion and subsequent denial of service. This CVE covers quadratic complexity issues when parsing text which leads with either large numbers of `_` characters. This issue has been addressed in version 0.29.0.gfm.10. Users are advised to upgrade. Users unable to upgrade should validate that their input comes from trusted sources. Impact A polynomial time complexity issue in cmark-gfm may lead to unbounded resource exhaustion and subsequent denial of service. Proof of concept ``` $ ~/cmark-gfm$ python3 -c 'pad = "_" * 100000; print(pad + "." + pad, end="")' | time ./build/src/cmark-gfm --to plaintext ``` Increasing the number 10000 in the above commands causes the running time to increase quadratically. Patches This vulnerability have been patched in 0.29.0.gfm.10. Note on cmark and cmark-gfm XXX: TBD cmark-gfm is a fork of cmark that adds the GitHub Flavored Markdown extensions. The two codebases have diverged over time, but share a common core. These bugs affect both `cmark` and `cmark-gfm`. Credit We would like to thank @gravypod for reporting this vulnerability. References https://en.wikipedia.org/wiki/Time_complexity For more information If you have any questions or comments about this advisory: • Open an issue in github/cmark-gfm

Timeline

1. Mar 31, 2023, 10:01 PM UTCCVE published
2. Feb 11, 2025, 5:20 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: yes · Technical impact: partial

3. Feb 11, 2025, 5:20 PM UTCRecord last updated

Affected versions

• github cmark-gfm

  fixed in 0.29.0.gfm.10

References 2