Vikunja: API token scopes bypassed via task expand parameter (comments, reactions, time entry counts)

{
  "id": "a2280ba68eb4201f0f50da45d0f2f1c2dbca44c880540505abf6c56eeac60f37",
  "url": "https://osv.dev/vulnerability/GHSA-9rg3-v78m-26q8",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Vikunja: API token scopes bypassed via task expand parameter (comments, reactions, time entry counts)",
    "summary": "## Summary API token permission checks only match the HTTP method and route path. The `expand` query parameter on task read endpoints embeds data from other permission groups (task comments, reactions, time entry counts) without checking whether the token holds those scopes. A token scoped only to `tasks` read permissions can therefore read task comments and reactions it was explicitly not granted. ## Details `models.CanDoAPIRoute` (`pkg/models/api_routes.go`, ~line 440) authorises API tokens purely by comparing `method` and `c.Path()` against the routes stored for each granted permission group. The query string is never consulted. The task read endpoints accept `expand`: - `GET /api/v1/tasks/:task`, `GET /api/v1/tasks` (`pkg/models/tasks.go` ReadOne/ReadAll, `pkg/models/task_collection.go`) - `GET /api/v2/tasks/:id`, `GET /api/v2/tasks`, `GET /api/v2/projects/:project/tasks` (`pkg/routes/api/v2/tasks.go`, `task_collection.go`) Accepted values include `comments`, `comment_count`, `reactions`, `time_entries_count`. `addMoreInfoToTasks` (`pkg/models/tasks.go`, ~line 683) loads and embeds that data. At that layer only a `web.Auth` (the plain owner user, resolved by `auth.GetAuthFromClaims`) is available, so the token's scopes cannot be enforced there either. Result: the `tasks_comments`, `reactions`, and `time_entries` permission groups are advisory for any data reachable through a task expansion. ## Impact A holder of an API token scoped to `tasks: [read_one]` or `tasks: [read_",
    "evidence": "osv:GHSA-9rg3-v78m-26q8",
    "products": [
      {
        "name": {
          "value": "code.vikunja.io/api",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "2.6.0",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "GHSA-9rg3-v78m-26q8",
      "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": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "1.0.0"
                },
                {
                  "fixed": "2.6.0"
                }
              ]
            }
          ],
          "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-9rg3-v78m-26q8/GHSA-9rg3-v78m-26q8.json",
            "last_known_affected_version_range": "<= 2.5.0"
          }
        }
      ],
      "modified": "2026-10-19T21:41:16.622292055Z",
      "provider": "osv",
      "references": [
        "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-9rg3-v78m-26q8",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-91983",
        "https://github.com/go-vikunja/vikunja/pull/3688",
        "https://github.com/go-vikunja/vikunja/commit/077dc4de79ce6f1ab59215a2c7bf9b30423685f2",
        "https://github.com/go-vikunja/vikunja",
        "https://github.com/go-vikunja/vikunja/releases/tag/v2.6.0",
        "https://www.vulncheck.com/advisories/vikunja-before-2.6.0-api-token-scope-bypass-via-expand-parameter"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-863"
        ],
        "severity": "MODERATE",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-09T20:51:52Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-91983",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 376793,
  "published_at": "2026-10-09T20:51:52+00:00"
}