Vikunja before 2.6.0 API Token Scope Bypass via expand Parameter

{
  "id": "b2ddf51becd1f2c60685710c86fc3c0544ac0b409b062d0241c067e32d300cee",
  "url": "https://osv.dev/vulnerability/CVE-2026-91983",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Vikunja before 2.6.0 API Token Scope Bypass via expand Parameter",
    "summary": "Vikunja before 2.6.0 contains an API token scope bypass vulnerability in task read endpoints where authorization fails to inspect query string parameters. Attackers with limited token scopes can use the expand parameter to access restricted data like comments, reactions, and time entries without proper permission verification.",
    "evidence": "osv:CVE-2026-91983",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-91983",
      "aliases": [
        "CVE-2026-91983",
        "GHSA-9rg3-v78m-26q8",
        "GO-2026-6726"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/go-vikunja/vikunja",
              "type": "GIT",
              "events": [
                {
                  "introduced": "3ba5192b1bd0607998bdaf9259d795fb14530384"
                },
                {
                  "fixed": "a4218eeb8fb3ada95e14a2331731524c9120d5bd"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "1.0.0"
                      },
                      {
                        "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"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-91983.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:39.551876839Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/91xxx/CVE-2026-91983.json",
        "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-9rg3-v78m-26q8",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-91983",
        "https://www.vulncheck.com/advisories/vikunja-before-2.6.0-api-token-scope-bypass-via-expand-parameter"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-863"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/91xxx/CVE-2026-91983.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-91983",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 507169,
  "published_at": "2026-09-15T15:18:26.899+00:00"
}