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Vikunja: Link-share token can enumerate users through the v2 APIGHSA-vfxw-3x8p-2vjr

Fix: go-vikunja/vikunja#3688

GHSA-vfxw-3x8p-2vjr is a Information Exposure vulnerability in code.vikunja.io/api. A fix is available for code.vikunja.io/api — see the affected versions and patch details below.

Also known asCVE-2026-91981GO-2026-6752
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for GHSA-vfxw-3x8p-2vjr.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs22th percentile — riskier than 22% of all scored CVEsHighest risk
0.00%0.27%0.54%0.81%0.3%0.3%Oct 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected
🐹code.vikunja.io/api

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

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 names), but that's still an instance-wide directory that a share-link holder should never see.

The fix is to resolve the caller with GetFromAuth in both handlers, so link-share tokens are rejected the same way v1 already rejects them.

PoC

  1. Get a link-share token. With any account that owns a project, create a read-only link share and note the hash, then exchange it:
POST /api/v1/shares/<hash>/auth
{"password":""}

The response contains a token, a link-share JWT.

  1. Confirm v1 blocks it (the fixed behavior). With that token:
GET /api/v1/projects/<id>/projectusers
Authorization: Bearer <link_share_token>

→ rejected: the token isn't a user token.

  1. Now the vulnerable v2 endpoints, same token:
GET /api/v2/projects/<id>/users/search
Authorization: Bearer <link_share_token>

→ 200, full list of everyone with access to the project and its parents (id, username, name).

GET /api/v2/users?q=admin
Authorization: Bearer <link_share_token>

→ 200, a non-empty result confirms the username exists on the instance. Iterate q over a wordlist to enumerate accounts.

Impact

Information disclosure. A link share is a low-trust credential meant to expose one project's contents; here it also exposes the membership of that project's parents and lets the holder probe for any username across the whole instance. Since share links are often forwarded or semi-public, this hands an untrusted recipient a map of internal users and a username-validation oracle useful for phishing and credential stuffing. No account is required beyond possessing a share link. Emails are not exposed.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gocode.vikunja.io/apiall versions2.6.0go get code.vikunja.io/api@v2.6.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for code.vikunja.io/api, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update code.vikunja.io/api to 2.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-vfxw-3x8p-2vjr is resolved across your whole dependency graph.

  3. Workarounds

    Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Frequently Asked Questions

### 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 pro
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Vikunja: Link-share token can enumerate users through…