Vikunja: Link-share principal ID collision allows cross-account API token issuance and management

{
  "id": "21c883f056fcb89d8805f8113b7a7f93d792ebfcc95e1912ea3258752eafaa5f",
  "url": "https://osv.dev/vulnerability/GHSA-vvcv-vpph-h844",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Vikunja: Link-share principal ID collision allows cross-account API token issuance and management",
    "summary": "Executive Summary Vikunja accepts both regular-user JSON Web Tokens (JWTs) and link-share JWTs through its generic authenticated API route group. A link-share JWT resolves to a `models.LinkSharing` principal whose `GetID()` method returns the numeric `link_shares.id`. The API-token management model then treats that generic numeric value as a `users.id` when it creates, lists, and deletes API tokens. Because `users.id` and `link_shares.id` are independent positive sequences, a link share whose ID equals another user's ID is treated as that user by `/api/v1/tokens`. An ordinary authenticated attacker can obtain a target's numeric user ID through authenticated user search and create link shares on an attacker-writable project until the link-share sequence reaches that value. The colliding link-share principal can then list the target's API-token metadata, issue a new API token owned by the target, and delete target-owned API tokens. The newly issued token operates with attacker-selected valid API scopes under the target user's existing permissions. I reviewed the vulnerable `v2.3.0` source, the introducing commit, the stable tag history, and the inspected main revision directly. I also reviewed the recorded local HTTP and native-router validation results. Dynamic testing used only a local `v2.3.0` Docker deployment with PostgreSQL and synthetic data; I did not test any public, hosted, or otherwise external instance. Historical tags were checked from source rather than exercised ",
    "evidence": "osv:GHSA-vvcv-vpph-h844",
    "products": [
      {
        "name": {
          "value": "code.vikunja.io/api",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "2.4.0",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "GHSA-vvcv-vpph-h844",
      "aliases": [
        "CVE-2026-68581",
        "GHSA-vvcv-vpph-h844",
        "GO-2026-6753"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0.22.0"
                },
                {
                  "fixed": "2.4.0"
                }
              ]
            }
          ],
          "package": {
            "name": "code.vikunja.io/api",
            "purl": "pkg:golang/code.vikunja.io/api",
            "ecosystem": "Go"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-vvcv-vpph-h844/GHSA-vvcv-vpph-h844.json",
            "last_known_affected_version_range": "<= 2.3.0"
          }
        }
      ],
      "modified": "2026-10-19T21:41:06.033854160Z",
      "provider": "osv",
      "references": [
        "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-vvcv-vpph-h844",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-68581",
        "https://github.com/go-vikunja/vikunja/commit/95b7e673fb5ee407498fa4b13e8b4c57847a4a0b",
        "https://github.com/go-vikunja/vikunja/commit/e6b25bd57b537ef9a72b5acdadf446ca5ef77bfa",
        "https://github.com/go-vikunja/vikunja",
        "https://github.com/go-vikunja/vikunja/releases/tag/v2.4.0",
        "https://www.vulncheck.com/advisories/vikunja-through-authentication-bypass-via-principal-id-collision"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-863"
        ],
        "severity": "HIGH",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-09T20:42:14Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-68581",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/database_specific/severity"
  },
  "source_id": "core-osv",
  "document_id": 376775,
  "published_at": "2026-10-09T20:42:14+00:00"
}