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CVE-2026-58399

Vulnerability in @acastellon/auth (CVE-2026-58399)

Summary

Vulnerability in @acastellon/auth (CVE-2026-58399). Risk of unauthorized operations or information disclosure. Exploitable via GET /protected. Mitigation: upgrade to 2.3.0 or later.

Original description

The description as published by the source.

@acastellon/auth v2.2.0 appears to allow an unauthenticated authentication bypass in validateToken() through spoofable auth-user and Host request headers.

The validateToken middleware contains a service-to-service bypass for auth-user: service-brother when req.get('host').startsWith(getHostName()). Both values involved in the check can be influenced by an unauthenticated HTTP client: auth-user is a request header, and Host is also client-controlled. As a result, a remote unauthenticated attacker can send a request with crafted headers and bypass token validation before the normal legacy/JWT/OIDC validation logic runs.

Impact:
An attacker may be able to access routes protected by validateToken() without a valid token. In deployments where downstream services trust auth-user or is-* headers, this may also lead to privilege escalation.

Affected package:
@acastellon/auth v2.2.0

Affected code:
auth.js, validateToken()
The issue is related to the service-brother bypass and getHostName() check.

Example request:

GET /protected HTTP/1.1
Host: 
auth-user: service-brother
is-admin: true

Expected behavior:
The request should require a valid authentication token.

Actual behavior:
The middleware calls next() before token validation.

Fix implemented in v2.3.0+:

Removed the spoofable bypass.
Always sanitize incoming auth-user and is-* headers.
Added mTLS client certificate based service auth (with optional TRUSTED_MTLS_SERVICES allowlist).
Updated consumers (rest, graphql, d…

Source: GitHub Security Advisories (Global) 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-2026-58399 has been found in @acastellon/auth.
Attackers can target a specific entry point like GET /protected over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade @acastellon/auth to 2.3.0 or later.
If unsure, ask your IT team or search "@acastellon/auth CVE-2026-58399" on the vendor's site.

CVE-2026-58399 (@acastellon/auth) — CWE-290
Attack surface: GET /protected
Patched: 2.3.0 — 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

A vulnerability (CWE-290) exists in @acastellon/auth. Attackers reach the vulnerable code path via GET /protected.

📍 Affected scope

Check the vendor advisory for the affected versions of @acastellon/auth. Attack surface: GET /protected.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 2.3.0.

🛡️ 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 /protected requests with malformed payloads or SQL meta-characters. Run grep -r '@acastellon/auth' . 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 '@acastellon/auth' . | 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 @acastellon/auth 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 /protected' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで GET /protected 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 @acastellon/auth to 2.3.0

    ステージング環境で 2.3.0 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 /protected 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

npm @acastellon/auth
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.3.0"}]}]

References

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