{"id":"CVE-2023-26485","url":"https://www.cyber-defence.io/tools/cve/CVE-2023-26485","generatedAt":"2026-10-24T17:58:05.969Z","title":"A polynomial time complexity issue in cmark-gfm may lead to unbounded resource exhaustion and subsequent denial of service.","description":"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","published":"2023-03-31T23:15:07.000Z","lastModified":"2026-06-17T05:43:26.000Z","status":"Modified","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"3.1","score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"cwe":["CWE-400","CWE-407"],"affected":["github/cmark-gfm"],"epss":{"score":0.01029,"percentile":0.634,"date":"2026-10-23","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (1.03%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://github.com/github/cmark-gfm/commit/07a66c9bc341f902878e37d7da8647d6ef150987","tags":["Patch"],"source":"security-advisories@github.com"},{"url":"https://github.com/github/cmark-gfm/security/advisories/GHSA-r8vr-c48j-fcc5","tags":["Exploit","Vendor Advisory"],"source":"security-advisories@github.com"},{"url":"https://github.com/github/cmark-gfm/commit/07a66c9bc341f902878e37d7da8647d6ef150987","tags":["Patch"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/github/cmark-gfm/security/advisories/GHSA-r8vr-c48j-fcc5","tags":["Exploit","Vendor Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2023-26485","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}