cmark-gfm: cmark-gfm is GitHub's fork of cmark, a CommonMark parsing and renderinglibrary and program in C

cmark-gfm is GitHub's fork of cmark, a CommonMark parsing and renderinglibrary and program in C. A polynomial time complexity issue in cmark-gfmmay lead to unbounded resource exhaustion and subsequent denial of service.This CVE covers quadratic complexity issues when parsing text which leadswith either large numbers of `_` characters. This issue has been addressedin version 0.29.0.gfm.10. Users are advised to upgrade. Users unable toupgrade should validate that their input comes from trusted sources.### ImpactA polynomial time complexity issue in cmark-gfm may lead to unboundedresource 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 timeto 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 FlavoredMarkdown extensions. The two codebases have diverged over time, but share acommon 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)

Where it's fixed