mistune — security advisory

{
  "id": "91a2d69e8a13276af83306800eb597752ab479a1ff8fee98c8f29f2a992cd94a",
  "url": "https://osv.dev/vulnerability/DEBIAN-CVE-2026-49851",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "DEBIAN-CVE-2026-49851",
    "summary": "Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.",
    "evidence": "osv:DEBIAN-CVE-2026-49851",
    "products": [
      {
        "name": {
          "value": "mistune",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": [
          {
            "value": "3.1.3-1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.1.4-1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.3.4-1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.4.0-1",
            "evidence": "/affected/0/versions"
          }
        ]
      },
      {
        "name": {
          "value": "mistune",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": [
          {
            "value": "3.1.3-1",
            "evidence": "/affected/1/versions"
          },
          {
            "value": "3.1.4-1",
            "evidence": "/affected/1/versions"
          },
          {
            "value": "3.3.4-1",
            "evidence": "/affected/1/versions"
          },
          {
            "value": "3.4.0-1",
            "evidence": "/affected/1/versions"
          }
        ]
      }
    ],
    "severity": "high",
    "structured": {
      "id": "DEBIAN-CVE-2026-49851",
      "aliases": [
        "DEBIAN-CVE-2026-49851"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                }
              ]
            }
          ],
          "package": {
            "name": "mistune",
            "purl": "pkg:deb/debian/mistune?arch=source&distro=trixie",
            "ecosystem": "Debian:13"
          },
          "versions": [
            "3.1.3-1",
            "3.1.4-1",
            "3.3.4-1",
            "3.4.0-1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-49851.json"
          },
          "ecosystem_specific": {
            "urgency": "not yet assigned"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                }
              ]
            }
          ],
          "package": {
            "name": "mistune",
            "purl": "pkg:deb/debian/mistune?arch=source&distro=forky",
            "ecosystem": "Debian:14"
          },
          "versions": [
            "3.1.3-1",
            "3.1.4-1",
            "3.3.4-1",
            "3.4.0-1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-49851.json"
          },
          "ecosystem_specific": {
            "urgency": "not yet assigned"
          }
        }
      ],
      "modified": "2026-10-26T12:02:57.894119510Z",
      "provider": "osv",
      "upstream": [
        "CVE-2026-49851"
      ],
      "references": [
        "https://security-tracker.debian.org/tracker/CVE-2026-49851"
      ]
    },
    "related_cves": [
      {
        "value": "CVE-2026-49851",
        "evidence": "/upstream"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 453016,
  "published_at": "2026-06-24T18:17:18.937+00:00"
}