Vikunja before 2.6.0 Authentication Bypass via CalDAV BasicAuth

{
  "id": "5da68f4dc790461558df1194af8213152fc5a663a18ebd76f7fbc7c64c402899",
  "url": "https://osv.dev/vulnerability/CVE-2026-91973",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Vikunja before 2.6.0 Authentication Bypass via CalDAV BasicAuth",
    "summary": "Vikunja before 2.6.0 contains an authentication bypass vulnerability in CalDAV BasicAuth endpoints that lack rate limiting protection. Remote unauthenticated attackers can issue unbounded credential-guessing requests against /dav, /.well-known, and /feeds routes to bypass the instance's anti-brute-force controls and compromise password-only accounts.",
    "evidence": "osv:CVE-2026-91973",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-91973",
      "aliases": [
        "CVE-2026-91973",
        "GHSA-m469-88xx-8rx2",
        "GO-2026-6737"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/go-vikunja/vikunja",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "a4218eeb8fb3ada95e14a2331731524c9120d5bd"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "2.6.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "2.6.0"
                      }
                    ],
                    "source": "DESCRIPTION"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v2.5.0",
            "v2.4.0",
            "v2.3.0",
            "v2.2.2",
            "v2.2.1",
            "v2.2.0",
            "v2.1.0",
            "v2.0.0",
            "v1.1.0",
            "v1.0.0",
            "v1.0.0-rc4",
            "v1.0.0-rc3",
            "v1.0.0-rc2",
            "v1.0.0-rc1",
            "v1.0.0-rc0",
            "v0.24.1",
            "v0.23.0",
            "v0.22.1",
            "v0.22.0",
            "v0.21.0",
            "v0.20.4",
            "v0.20.3",
            "v0.20.1",
            "v0.20.0",
            "v0.19.2",
            "v0.19.1",
            "v0.19.0",
            "v0.18.1",
            "v0.18.0",
            "v0.17.0",
            "v0.16.0",
            "v0.15.0",
            "v0.14.0",
            "v0.13",
            "v0.12",
            "v0.11",
            "v0.10",
            "v0.9",
            "v0.8",
            "v0.7",
            "v0.6",
            "v0.5",
            "v0.4",
            "v0.3",
            "v0.2",
            "v0.1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-91973.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:51.699821502Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/91xxx/CVE-2026-91973.json",
        "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-m469-88xx-8rx2",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-91973",
        "https://www.vulncheck.com/advisories/vikunja-before-2.6.0-authentication-bypass-via-caldav-basicauth"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-307"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/91xxx/CVE-2026-91973.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-91973",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 520339,
  "published_at": "2026-09-15T15:18:23.488+00:00"
}