Cmark Gfm CVE-2023-26485

This vulnerability is classified as Uncontrolled Resource Consumption (CWE-400), which allows attackers to cause denial of service by exhausting system resources. 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 Affected products include: Github Cmark-Gfm. Version information: version 0.29.0..