Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions

{
  "id": "08ff37f6003bb75e9bd4961d27b8d0965b01d9c475511d2cf9c2e73e394b784f",
  "url": "https://osv.dev/vulnerability/CVE-2026-59928",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions",
    "summary": "Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown document containing many repeated or distinct reference-link definitions causes quadratic work in src/mistune/block_parser.py and the ref_links environment dictionary handling, allowing denial of service through CPU exhaustion. This issue is fixed in version 3.3.0.",
    "evidence": "osv:CVE-2026-59928",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-59928",
      "aliases": [
        "CVE-2026-59928",
        "GHSA-ffq3-xpv3-j92q",
        "PYSEC-2026-2216"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/lepture/mistune",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "15c3b79325125272263d7d42492ec8f757447191"
                },
                {
                  "fixed": "2b04d7ba341c16ac78fe82d3076bdd5c3de87c69"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "3.3.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "2b04d7ba341c16ac78fe82d3076bdd5c3de87c69"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "15c3b79325125272263d7d42492ec8f757447191"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v3.3.0"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v3.2.1",
            "v3.2.0",
            "v3.1.4",
            "v3.1.3",
            "v3.1.2",
            "v3.1.1",
            "v3.1.0",
            "v3.0.1",
            "v3.0.0",
            "v3.0.0rc5",
            "v3.0.0rc4",
            "v3.0.0rc3",
            "v3.0.0rc2",
            "v3.0.0rc1",
            "v3.0.0a3",
            "v3.0.0a2",
            "v3.0.0a1",
            "v2.0.2",
            "v2.0.1",
            "v2.0.0",
            "v2.0.0rc1",
            "v2.0.0a6",
            "v2.0.0a5",
            "v2.0.0a4",
            "v2.0.0a3",
            "v2.0.0a2",
            "v2.0.0a1",
            "v0.8.4",
            "v0.8.3",
            "v0.8.2",
            "v0.8.1",
            "v0.8",
            "v0.7.4",
            "v0.7.3",
            "v0.7.2",
            "v0.7.1",
            "v0.7",
            "v0.6",
            "v0.5.1",
            "v0.5",
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            "v0.4",
            "v0.3.1",
            "v0.3.0",
            "v0.2.0",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-59928.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:50.939571656Z",
      "provider": "osv",
      "references": [
        "https://github.com/lepture/mistune/releases/tag/v3.3.0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59928.json",
        "https://github.com/lepture/mistune/security/advisories/GHSA-ffq3-xpv3-j92q",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-59928",
        "https://github.com/lepture/mistune/commit/2b04d7ba341c16ac78fe82d3076bdd5c3de87c69"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-1333",
          "CWE-407"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59928.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-59928",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 519555,
  "published_at": "2026-07-08T16:23:21+00:00"
}