Vikunja: Link-share token can enumerate users through the v2 API

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-91981: 0.31% estimated exploitation activity in the next 30 days; percentile 23.49 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A link-share token, the credential you hand out to let someone view a shared project, can call the v2 user-search endpoints, which it was never meant to reach. The v1 versions of the same endpoints correctly reject link-share tokens; the v2 versions don't. As a result, anyone with a share link can list every member of the shared project (and its parent projects), and can test whether any username exists anywhere on the instance. Details Two endpoints are affected: GET /api/v2/projects/{id}/users/search only checks project.CanRead, which a link share satisfies on its own project. With no parameter it returns the full user list, walking up the parent-project chain. GET /api/v2/users?q=<name is a global search. It needs a query term, but any term works as an existence oracle: a hit confirms the username exists somewhere on the instance and returns the display name. Emails are correctly stripped from these responses, so the exposure is limited to identities (usernames and display…

Published by the source

9 Oct 2026, 20:52 UTC

Last modified by the source

19 Oct 2026, 21:31 UTC

Source last checked

26 Oct 2026, 15:32 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vfxw-3x8p-2vjr

2. Revision 3 · amended · 25 Oct 2026

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

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GO-2026-6752

4. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-vfxw-3x8p-2vjr

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# Patch Next advisory brief: CVE-2026-91981

Advisory: Vikunja: Link-share token can enumerate users through the v2 API
IDs: CVE-2026-91981, GHSA-vfxw-3x8p-2vjr
Record: https://patchnext.com/advisories/cve-2026-91981 (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 5.3)
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-2026-6752 (OSV record GO-2026-6752 lists affected ranges: Go code.vikunja.io/api >=0)
- Verified: https://osv.dev/vulnerability/GHSA-vfxw-3x8p-2vjr (OSV record GHSA-vfxw-3x8p-2vjr lists affected ranges: Go code.vikunja.io/api >=0 <2.6.0 (fixed))
- Verified: https://github.com/advisories/GHSA-vfxw-3x8p-2vjr (GitHub-reviewed advisory GHSA-vfxw-3x8p-2vjr lists affected ranges: Go code.vikunja.io/api >=0 <=2.5.0)

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