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

Advisory record · `GHSA-g38j-7v97-x298`

- **Identifiers:** `GHSA-g38j-7v97-x298` · `GO-2026-6732`
- **State:** Confirmed
- **Severity:** CVSS 4.0, no score published
- **Critical:** No
- **Weakness (CWE):** [CWE-862](https://cwe.mitre.org/data/definitions/862.html)
- **Tags:** [Broken access control](https://agentprime.io/advisories/tag/access-control.md)
- **Published:** 9 Oct 2026
- **Updated:** 19 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 9 Oct 2026, 20:54 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `code.vikunja.io/api` (Go): affected `<2.6.0`; fixed in `2.6.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Vikunja versions before 2.6.0 let an authenticated user create task relations through CalDAV without the permission check the REST API enforces. An attacker who knows the UID of a task, including one in a project they cannot access, can attach a subtask or parent relation to it, which is an unauthorized write. Upgrade to Vikunja 2.6.0 or later, which fixes this.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- Score not published, CVSS 4.0: `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`, from GitHub Advisory Database

- **CISA KEV:** Not listed.
- **EPSS:** No score.

## Timeline

- 31 Oct 2026, 14:11 UTC: First seen by agentprime
- 31 Oct 2026, 14:11 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-g38j-7v97-x298)

## Sources

- [GitHub Advisory Database: GHSA-g38j-7v97-x298](https://github.com/advisories/GHSA-g38j-7v97-x298)
- [OSV: GHSA-g38j-7v97-x298](https://osv.dev/vulnerability/GHSA-g38j-7v97-x298)
- <https://github.com/go-vikunja/vikunja/security/advisories/GHSA-g38j-7v97-x298>
- <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>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-g38j-7v97-x298>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-g38j-7v97-x298/>. Everything for agents: <https://agentprime.io/llms.txt>.