{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.5.0"
      },
      "package": {
        "ecosystem": "Go",
        "name": "code.vikunja.io/api"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.9"
            },
            {
              "fixed": "2.6.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-285",
      "CWE-862"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-09T20:54:52Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "## Summary\n\nDeleting a task relation only requires write access on the base task. Unlike relation creation, it does not verify that the caller can read the other task. A user with write access to one project can therefore delete relations whose other end lives in a project they have no access to. Since the delete removes both the forward and inverse rows, the relation also disappears for the other project\u0027s members.\n\n## Details\n\n`TaskRelation.CanCreate` (`pkg/models/task_relation_permissions.go:32-52`) requires write access on `TaskID` **and** read access on `OtherTaskID`.\n\n`TaskRelation.CanDelete` (`pkg/models/task_relation_permissions.go:25-29`) only checks `Task{ID: rel.TaskID}.CanUpdate(s, a)`; `OtherTaskID` is never authorized.\n\n`TaskRelation.Delete` (`pkg/models/task_relation.go:314-354`) then deletes both the `(task_id, other_task_id, kind)` row and its inverse, so the relation is removed from the far task as well.\n\nAffects `DELETE /api/v1/tasks/{id}/relations/{kind}/{otherTaskId}` and the equivalent v2 endpoint.\n\n## Impact\n\nLow, integrity only. An authenticated user holding write permission on a shared project can remove task relations that link into projects they cannot read. No data is disclosed and no privilege is gained; the attacker cannot recreate the relation. The far project\u0027s owner sees the relation vanish without indication of who removed it.\n\nPreconditions: the attacker has write access to a project containing a task that is already related to a task in a project they cannot access.\n\n## Proof of Concept\n\n1. As `owner`, create project `P_near` with task `near` and project `P_far` with task `far`.\n2. Share `P_near` with `attacker` at write permission (`permission: 1`). Do not share `P_far`.\n3. As `owner`: `PUT /api/v1/tasks/{near}/relations` with `{\"other_task_id\": far, \"relation_kind\": \"related\"}` -\u003e 200.\n4. As `attacker`: `GET /api/v1/tasks/{far}` -\u003e 403 (confirms no access).\n5. As `attacker`: `PUT /api/v1/tasks/{near}/relations` with the same body -\u003e 403 (create path is enforced).\n6. As `attacker`: `DELETE /api/v1/tasks/{near}/relations/related/{far}` -\u003e 200 `\"Successfully deleted.\"`\n7. As `owner`: `GET /api/v1/tasks/{far}` -\u003e `related_tasks` is now empty.\n\nReproduced against `vikunja/vikunja:2.5.0`.\n\n## Recommended Fix\n\nMake `CanDelete` mirror `CanCreate`: after checking `CanUpdate` on the base task, also require `CanRead` on `OtherTaskID`.",
  "id": "GHSA-w2ch-4xgr-22ww",
  "modified": "2026-10-09T20:54:52Z",
  "published": "2026-10-09T20:54:52Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-w2ch-4xgr-22ww"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/pull/3688"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/commit/077dc4de79ce6f1ab59215a2c7bf9b30423685f2"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/go-vikunja/vikunja"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/releases/tag/v2.6.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Vikunja: Task relation deletion does not check read access to the other task, allowing cross-project relation removal"
}