{"id":"CVE-2023-26485","summary":"Quadratic complexity may lead to a denial of service in cmark-gfm","details":"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.\n\n\n\n\n### Impact\n\nA polynomial time complexity issue in cmark-gfm may lead to unbounded resource exhaustion and subsequent denial of service.\n\n### Proof of concept\n\n```\n$ ~/cmark-gfm$ python3 -c 'pad = \"_\" * 100000; print(pad + \".\" + pad, end=\"\")' | time ./build/src/cmark-gfm --to plaintext\n```\n\nIncreasing the number 10000 in the above commands causes the running time to increase quadratically.\n\n### Patches\n\nThis vulnerability have been patched in 0.29.0.gfm.10.\n\n### Note on cmark and cmark-gfm\n\nXXX: TBD\n\n[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`. \n\n### Credit\n\nWe would like to thank @gravypod for reporting this vulnerability.\n\n### References\n\nhttps://en.wikipedia.org/wiki/Time_complexity\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n\n* Open an issue in [github/cmark-gfm](https://github.com/github/cmark-gfm)\n","aliases":["GHSA-r8vr-c48j-fcc5"],"modified":"2026-04-10T04:56:23.493215Z","published":"2023-03-31T22:01:16.350Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/26xxx/CVE-2023-26485.json","cwe_ids":["CWE-400","CWE-407"],"cna_assigner":"GitHub_M"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/26xxx/CVE-2023-26485.json"},{"type":"ADVISORY","url":"https://github.com/github/cmark-gfm/security/advisories/GHSA-r8vr-c48j-fcc5"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2023-26485"},{"type":"FIX","url":"https://github.com/github/cmark-gfm/commit/07a66c9bc341f902878e37d7da8647d6ef150987"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/github/cmark-gfm","events":[{"introduced":"0"},{"fixed":"dcf6b3862d2885b7d3dcdfc5b30c6a73526be32c"}]}],"versions":["0.27.1.gfm.2","0.27.1.gfm.3","0.27.1.gfm.4","0.28.0.gfm.10","0.28.0.gfm.11","0.28.0.gfm.5","0.28.0.gfm.6","0.28.0.gfm.7","0.28.0.gfm.8","0.28.0.gfm.9","0.28.3.gfm.12","0.28.3.gfm.13","0.28.3.gfm.14","0.28.3.gfm.15","0.28.3.gfm.16","0.28.3.gfm.17","0.28.3.gfm.18","0.28.3.gfm.19","0.28.3.gfm.20","0.29.0.gfm.0","0.29.0.gfm.1","0.29.0.gfm.2","0.29.0.gfm.3","0.29.0.gfm.4","0.29.0.gfm.5","0.29.0.gfm.6","0.29.0.gfm.7","0.29.0.gfm.8","0.29.0.gfm.9"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2023-26485.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"}]}