Quadratic complexity may lead to a denial of service in cmark-gfm

{
  "id": "693ad9198e426db737de8b50e3b0e8b31631a51ce52d44bad024427170cffd70",
  "url": "https://osv.dev/vulnerability/CVE-2023-26485",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Quadratic complexity may lead to a denial of service in cmark-gfm",
    "summary": "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 advis",
    "evidence": "osv:CVE-2023-26485",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2023-26485",
      "aliases": [
        "CVE-2023-26485",
        "GHSA-r8vr-c48j-fcc5"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/github/cmark-gfm",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "dcf6b3862d2885b7d3dcdfc5b30c6a73526be32c"
                },
                {
                  "fixed": "07a66c9bc341f902878e37d7da8647d6ef150987"
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              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:github:cmark-gfm:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
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                      {
                        "fixed": "0.29.0.gfm.10"
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                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "07a66c9bc341f902878e37d7da8647d6ef150987"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "0.29.0.gfm.9",
            "0.29.0.gfm.8",
            "0.29.0.gfm.7",
            "0.29.0.gfm.6",
            "0.29.0.gfm.5",
            "0.29.0.gfm.4",
            "0.29.0.gfm.3",
            "0.28.3.gfm.20",
            "0.29.0.gfm.2",
            "0.29.0.gfm.1",
            "0.29.0.gfm.0",
            "0.28.3.gfm.19",
            "0.28.3.gfm.18",
            "0.28.3.gfm.17",
            "0.28.3.gfm.16",
            "0.28.3.gfm.15",
            "0.28.3.gfm.14",
            "0.28.3.gfm.13",
            "0.28.3.gfm.12",
            "0.28.0.gfm.11",
            "0.28.0.gfm.10",
            "0.28.0.gfm.9",
            "0.28.0.gfm.8",
            "0.28.0.gfm.7",
            "0.28.0.gfm.6",
            "0.28.0.gfm.5",
            "0.27.1.gfm.4",
            "0.27.1.gfm.3",
            "0.27.1.gfm.2"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2023-26485.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:22.417351927Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/26xxx/CVE-2023-26485.json",
        "https://github.com/github/cmark-gfm/security/advisories/GHSA-r8vr-c48j-fcc5",
        "https://nvd.nist.gov/vuln/detail/CVE-2023-26485",
        "https://github.com/github/cmark-gfm/commit/07a66c9bc341f902878e37d7da8647d6ef150987"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-400",
          "CWE-407"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/26xxx/CVE-2023-26485.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2023-26485",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 488534,
  "published_at": "2023-03-31T22:01:16.35+00:00"
}