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. ### 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)

References:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2023-26485
https://www.cve.org/CVERecord?id=CVE-2023-26485
http://www.cvedetails.com/cve/CVE-2023-26485/
https://github.com/github/cmark-gfm/commit/07a66c9bc341f902878e37d7da8647d6ef150987
https://github.com/github/cmark-gfm/security/advisories/GHSA-r8vr-c48j-fcc5