Vikunja: Cross-tenant task-position rows can be injected into arbitrary project views via the unvalidated project_view_id in the task position endpoint (v1 and v2)

{
  "id": "7ccab682a7e7d30d5ca50fc33b3c9a28351e77abff325acab51ca67188646cb4",
  "url": "https://osv.dev/vulnerability/GHSA-w39f-h553-h2mx",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Vikunja: Cross-tenant task-position rows can be injected into arbitrary project views via the unvalidated project_view_id in the task position endpoint (v1 and v2)",
    "summary": "## Summary The task-position endpoint authorizes only the task side of the write: `TaskPosition.CanUpdate` delegates to `Task.CanUpdate` (write access to the task's own project) and the request body's `project_view_id` is never validated to belong to the task's project, nor is any access to that view required. Any authenticated user with a single writable task of their own can persist `(task_id, project_view_id, position)` rows into any other tenant's project view (view IDs are small sequential integers and enumerable). Low position values (below `MinPositionSpacing`, 0.01) enter the recalculation branch, but `RecalculateTaskPositions` aborts on its own project read-access check before recalculating and the whole transaction rolls back, so no cross-tenant recalculation actually executes — only the plain row insert (position ≥ 0.01) persists. This is the same root-cause pattern as GHSA-569v-q83c-3j3g (kanban bucket relocation via project_view_id mass-assignment, fixed with a dual-side check for buckets in 2.4.0) surviving in the sibling position endpoint. Verified on Vikunja 2.5.0. ## Details Affected endpoints (both verified): - v1: `POST /api/v1/tasks/{id}/position` - v2: `PUT /api/v2/tasks/{id}/position` Root cause in `pkg/models/task_position.go`: - `CanUpdate` (lines 61-64) checks only `Task.CanUpdate` — i.e. the caller's write access to the task's own project. - `updateTaskPosition` (lines 174-232) upserts `(task_id, project_view_id, position)` directly; there is no chec",
    "evidence": "osv:GHSA-w39f-h553-h2mx",
    "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-w39f-h553-h2mx",
      "aliases": [
        "CVE-2026-91984",
        "GHSA-w39f-h553-h2mx",
        "GO-2026-6755"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "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-w39f-h553-h2mx/GHSA-w39f-h553-h2mx.json",
            "last_known_affected_version_range": "<= 2.5.0"
          }
        }
      ],
      "modified": "2026-10-19T21:40:58.721073742Z",
      "provider": "osv",
      "references": [
        "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-w39f-h553-h2mx",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-91984",
        "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-broken-object-level-authorization-via-task-position"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-639",
          "CWE-863"
        ],
        "severity": "MODERATE",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-09T20:51:41Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-91984",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 376764,
  "published_at": "2026-10-09T20:51:41+00:00"
}