CVE-2023-26485
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.### ImpactA 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.### PatchesThis vulnerability have been patched in 0.29.0.gfm.10.### Note on cmark and cmark-gfmXXX: TBD[cmark-gfm](https://github.com/github/cmark-gfm) is a fork of [cmark](https://github.com/commonmark/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`. ### CreditWe would like to thank @gravypod for reporting this vulnerability.### Referenceshttps://en.wikipedia.org/wiki/Time_complexity### For more informationIf you have any questions or comments about this advisory:* Open an issue in [github/cmark-gfm](https://github.com/github/cmark-gfm)
- CVSS v3.1
- 7.5 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - CVSS v3.1
- 5.3 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - EPSS
- 1.03% chance of exploitation in the next 30 days, 61th percentile
- Published
- 2023-03-31
- Updated
- 2025-02-11