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CVE-2026-91981 medium CVSS 4.3

Information Disclosure in code.vikunja.io/api (CVE-2026-91981)

Summary

Vulnerability in code.vikunja.io/api (CVE-2026-91981). Risk of unauthorized operations or information disclosure. Exploitable via GET /api/v2/projects/{id}/users/search. Mitigation: upgrade to 2.6.0 or later.

Original description

The description as published by the source.

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= 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//auth
{"password":""}

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

  1. Confirm v1…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-91981 has been found in code.vikunja.io/api.
Attackers can target a specific entry point like GET /api/v2/projects/{id}/users/search over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 4.3/10.
What to do: upgrade code.vikunja.io/api to 2.6.0 or later.
If unsure, ask your IT team or search "code.vikunja.io/api CVE-2026-91981" on the vendor's site.

CVE-2026-91981 (code.vikunja.io/api) — CWE-200 / CVSS v3 4.3
Attack vector: remote (network-reachable) / no user interaction
Attack surface: GET /api/v2/projects/{id}/users/search / GET /api/v2/users / POST /api/v1/shares/ / GET /api/v1/projects/
Patched: 2.6.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Information disclosure (CWE-200) exists in code.vikunja.io/api. Attackers reach the vulnerable code path via GET /api/v2/projects/{id}/users/search.

📍 Affected scope

Check the vendor advisory for the affected versions of code.vikunja.io/api. Attack surface: GET /api/v2/projects/{id}/users/search / GET /api/v2/users / POST /api/v1/shares/ / GET /api/v1/projects/.

🔥 Severity

Severity: Medium (CVSS 4.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 2.6.0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual GET /api/v2/projects/{id}/users/search requests with malformed payloads or SQL meta-characters. Run grep -r 'code.vikunja.io/api' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'code.vikunja.io/api' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で code.vikunja.io/api を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Hunt for indicators of compromise detect 
    grep 'GET /api/v2/projects/{id}/users/search' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで GET /api/v2/projects/{id}/users/search への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。

  3. 3
    Apply patch patch 
    Upgrade code.vikunja.io/api to 2.6.0

    ステージング環境で 2.6.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスと、Step 2 で見つけた異常検知の続報チェックを含めること。

  4. 4
    Post-deployment verification verify 
    Replay attack against GET /api/v2/projects/{id}/users/search on staging to confirm patch closes the vector

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番では Step 2 と同じログクエリでアラート再発が無いか継続監視。

Affected packages

go code.vikunja.io/api
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.6.0"}]}]

References

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