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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 `>` or `-` 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.
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](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`.
### 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](https://github.com/github/cmark-gfm)
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cmark-gfm is GitHub's fork of cmark, a CommonMark parsing and rendering library and program in C. Versions prior to 0.29.0.gfm.7 are subject to several polynomial time complexity issues in cmark-gfm that may lead to unbounded resource exhaustion and subsequent denial of service. Various commands, when piped to cmark-gfm with large values, cause the running time to increase quadratically. These vulnerabilities have been patched in version 0.29.0.gfm.7.