{"id":"GHSA-w2ch-4xgr-22ww","title":"Vikunja: Task relation deletion does not check read access to the other task, allowing cross-project relation removal","summary":"Vikunja: Task relation deletion does not check read access to the other task, allowing cross-project relation removal","severity":"low","cwe":["CWE-285","CWE-862"],"vendor":"api","product":"code.vikunja.io/api","ecosystem":"go","affected":["code.vikunja.io/api >= 0.9, <= 2.5.0"],"patched":["code.vikunja.io/api 2.6.0"],"published":"2026-10-09","updated":"2026-10-09","sourceUpdated":"2026-10-09T20:54:52Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-w2ch-4xgr-22ww","references":[{"url":"https://github.com/go-vikunja/vikunja/security/advisories/GHSA-w2ch-4xgr-22ww"},{"url":"https://github.com/go-vikunja/vikunja/pull/3688"},{"url":"https://github.com/go-vikunja/vikunja/commit/077dc4de79ce6f1ab59215a2c7bf9b30423685f2"},{"url":"https://github.com/go-vikunja/vikunja/releases/tag/v2.6.0"},{"url":"https://github.com/advisories/GHSA-w2ch-4xgr-22ww"}],"tags":["ghsa","go"],"ingestedAt":"2026-10-09T21:12:42.323Z","slug":"GHSA-w2ch-4xgr-22ww","body":"## Overview\n\n## 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's 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's 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\"}` -> 200.\n4. As `attacker`: `GET /api/v1/tasks/{far}` -> 403 (confirms no access).\n5. As `attacker`: `PUT /api/v1/tasks/{near}/relations` with the same body -> 403 (create path is enforced).\n6. As `attacker`: `DELETE /api/v1/tasks/{near}/relations/related/{far}` -> 200 `\"Successfully deleted.\"`\n7. As `owner`: `GET /api/v1/tasks/{far}` -> `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`.\n\n## Affected packages\n\n- `code.vikunja.io/api >= 0.9, <= 2.5.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `code.vikunja.io/api 2.6.0`","depth":"sunlit","depthScore":14,"depthScoreParts":{"impact":13.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}