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Medium, CVSS 6.3amended

Vikunja: CalDAV relation creation bypasses TaskRelation.CanCreate, allowing an unauthorized write into any task by known UID

GHSA-g38j-7v97-x298

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (code.vikunja.io/api 2.6.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.3 · CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N · score source
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

Summary Creating a task relation over CalDAV does not run the TaskRelation.CanCreate permission check that the REST API enforces. An attacker can attach a relation to any task whose UID they know, including tasks in projects they have no access to. The identical operation over REST is correctly refused with 403. Details persistRelations (pkg/routes/caldav/listStorageProvider.go, ~line 986) resolves the related task with an unscoped UID lookup (models.GetTaskSimpleByUUID) and calls rel.Create(s, a) directly, with no CanCreate check. pkg/caldav/parsing.go maps RELATED-TO;RELTYPE=CHILD to RelationKindSubtask. Because the CalDAV path never invokes the model's permission method, an authenticated user can create a subtask/parent relation between a task they own and an arbitrary victim task identified only by its UID. Task UIDs are json:"-" (never exposed over REST) but are exposed over CalDAV to anyone who has ever had read access to the containing project. Revoking that access does not…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-g38j-7v97-x298

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record GO-2026-6732

  4. Revision 1 · created ·

    Published from osv record GHSA-g38j-7v97-x298

Agent brief

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# Patch Next advisory brief: GHSA-g38j-7v97-x298

Advisory: Vikunja: CalDAV relation creation bypasses TaskRelation.CanCreate, allowing an unauthorized write into any task by known UID
IDs: GHSA-g38j-7v97-x298
Record: https://patchnext.com/advisories/ghsa-g38j-7v97-x298 (revision 4, source checked 26 Oct 2026, 15:32 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: code.vikunja.io/api 2.6.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go code.vikunja.io/api: affected <= 2.5.0; fixed in 2.6.0

## Suggested inspection (read-only)
- Go code.vikunja.io/api: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on code.vikunja.io/api.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GO-2026-6732 (OSV record GO-2026-6732 lists affected ranges: Go code.vikunja.io/api >=0)
- Verified: https://osv.dev/vulnerability/GHSA-g38j-7v97-x298 (OSV record GHSA-g38j-7v97-x298 lists affected ranges: Go code.vikunja.io/api >=0 <2.6.0 (fixed))
- Verified: https://github.com/advisories/GHSA-g38j-7v97-x298 (GitHub-reviewed advisory GHSA-g38j-7v97-x298 lists affected ranges: Go code.vikunja.io/api >=0 <=2.5.0)

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