Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing

{
  "id": "e034900c0e064be0dd8b73dea033b38a866ea1d12e676e267dcba5d2324356b6",
  "url": "https://www.cve.org/CVERecord?id=CVE-2026-115349",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing",
    "summary": "Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.",
    "evidence": "cve:CVE-2026-115349",
    "products": [
      {
        "name": {
          "value": "mistune",
          "evidence": "/containers/cna/affected/0/product"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-115349",
      "aliases": [
        "CVE-2026-115349"
      ],
      "metrics": [
        {
          "format": "CVSS",
          "cvssV4_0": {
            "version": "4.0",
            "baseScore": 8.7,
            "attackVector": "NETWORK",
            "baseSeverity": "HIGH",
            "vectorString": "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",
            "userInteraction": "NONE",
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "privilegesRequired": "NONE",
            "subIntegrityImpact": "NONE",
            "vulnIntegrityImpact": "NONE",
            "subAvailabilityImpact": "NONE",
            "vulnAvailabilityImpact": "HIGH",
            "subConfidentialityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE"
          }
        },
        {
          "format": "CVSS",
          "cvssV3_1": {
            "scope": "UNCHANGED",
            "version": "3.1",
            "baseScore": 7.5,
            "attackVector": "NETWORK",
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "integrityImpact": "NONE",
            "userInteraction": "NONE",
            "attackComplexity": "LOW",
            "availabilityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "confidentialityImpact": "NONE"
          }
        }
      ],
      "affected": [
        {
          "vendor": "lepture",
          "product": "mistune",
          "versions": [
            {
              "status": "affected",
              "version": "3.0.0",
              "lessThan": "3.3.0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "3.3.0",
              "versionType": "semver"
            }
          ],
          "packageURL": "pkg:pypi/mistune",
          "defaultStatus": "unaffected"
        }
      ],
      "modified": "2026-10-26T19:38:30.354Z",
      "provider": "cve",
      "references": [
        "https://github.com/lepture/mistune/security/advisories/GHSA-3q64-rw38-243v",
        "https://www.vulncheck.com/advisories/mistune-3.0.0-before-3.3.0-denial-of-service-via-nested-bracket-parsing"
      ],
      "provider_metadata": {
        "adp": [
          {
            "title": "CISA ADP Vulnrichment",
            "metrics": [
              {
                "other": {
                  "type": "ssvc",
                  "content": {
                    "id": "CVE-2026-115349",
                    "role": "CISA Coordinator",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "yes"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "version": "2.0.3",
                    "timestamp": "2026-10-26T19:27:03.150656Z"
                  }
                }
              }
            ],
            "providerMetadata": {
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP",
              "dateUpdated": "2026-10-26T19:38:30.354Z"
            }
          }
        ],
        "cna": {
          "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
          "shortName": "VulnCheck",
          "dateUpdated": "2026-10-22T19:13:26.171Z"
        }
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-115349",
        "evidence": "/cveMetadata/cveId"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/containers/cna/metrics"
  },
  "source_id": "core-cve",
  "document_id": 338247,
  "published_at": "2026-10-22T19:13:26.171+00:00"
}