CVE-2026-58399: @acastellon/auth Authentication Bypass Vulnerability

CRITICAL
Advisory Identifier: GHSA-gfj5-979r-92pw
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CWE-290
Published
Advisory Summary

CVE-2026-58399 is a CRITICAL authentication bypass vulnerability (CWE-290: Authentication Bypass by Spoofing) affecting @acastellon/auth libraries in the npm ecosystem. The issue involves authentication bypass via spoofable headers in validatetoken(). Remediation is available by upgrading affected packages to version 2.3.0.

CVE-2026-58399 at a Glance

CVE Identifier CVE-2026-58399
GHSA Identifier GHSA-gfj5-979r-92pw
Severity CRITICAL
CVSS v3.1 Base Score N/A
CWE Classification CWE-290: Authentication Bypass by Spoofing
Affected Product @acastellon/auth
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-58399

To remediate this vulnerability, upgrade all affected @acastellon/auth dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

@acastellon/auth fixed: 2.3.0 
npm install @acastellon/auth@2.3.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls @acastellon/auth

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-58399, inspect your project dependencies using npm:

npm ls @acastellon/auth

Analyze the terminal output to locate any version of @acastellon/auth in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.3.0), your application is affected.

Note: The npm ls @acastellon/auth command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-290: Authentication Bypass by Spoofing, where this attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks. In @acastellon/auth, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

@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: <configured CNAME or hostname> 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, dns-client) for mTLS support. Unit tests added for sanitization + mTLS path.

CVE-2026-58399 Affected @acastellon/auth Versions

1 component(s)
Fixed Versions:
2.3.0
Product / Package Ecosystem Affected Versions Fixed Version
@acastellon/auth
npm/@acastellon/auth
npm
< 2.3.0
2.3.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/antonio-castellon/module-auth/security/advisories/GHSA-gfj5-979r-92pw
@acastellon/auth Source Repository REPOSITORY
https://github.com/antonio-castellon/module-auth/issues/6
@acastellon/auth Source Repository REPOSITORY
https://github.com/antonio-castellon/module-auth
www.npmjs.com/package/@acastellon... WEB
https://www.npmjs.com/package/@acastellon/auth/v/2.3.0

Frequently Asked Questions

What is CVE-2026-58399?
CVE-2026-58399 is a security vulnerability in @acastellon/auth involving Authentication bypass via spoofable headers in validateToken() under CWE-290: Authentication Bypass by Spoofing.
Which @acastellon/auth versions are affected?
Affected versions include releases prior to 2.3.0 across affected packages: @acastellon/auth.
What version fixes CVE-2026-58399?
Upgrading to 2.3.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is @acastellon/auth affected?
Yes, @acastellon/auth is affected in releases prior to 2.3.0. Upgrade your dependency to 2.3.0 or later.
What CWE is associated with CVE-2026-58399?
CVE-2026-58399 is classified under CWE-290: Authentication Bypass by Spoofing (This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.).
How can I check npm dependencies for CVE-2026-58399?
Run the dependency tree command: 'npm ls @acastellon/auth'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-gfj5-979r-92pw",
  "modified" : "2026-07-01T14:30:32Z",
  "published" : "2026-06-18T17:22:47Z",
  "aliases" : [ "CVE-2026-58399" ],
  "summary" : "@acastellon/auth: Authentication bypass via spoofable headers in validateToken()",
  "details" : "@acastellon/auth v2.2.0 appears to allow an unauthenticated authentication bypass in validateToken() through spoofable auth-user and Host request headers.\n\nThe 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.\n\nImpact:\nAn 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.\n\nAffected package:\n@acastellon/auth v2.2.0\n\nAffected code:\nauth.js, validateToken()\nThe issue is related to the service-brother bypass and getHostName() check.\n\nExample request:\n```\nGET /protected HTTP/1.1\nHost: <configured CNAME or hostname>\nauth-user: service-brother\nis-admin: true\n```\n\nExpected behavior:\nThe request should require a valid authentication token.\n\nActual behavior:\nThe middleware calls next() before token validation.\n\nFix implemented in v2.3.0+:\n\nRemoved the spoofable bypass.\nAlways sanitize incoming auth-user and is-* headers.\nAdded mTLS client certificate based service auth (with optional TRUSTED_MTLS_SERVICES allowlist).\nUpdated consumers (rest, graphql, dns-client) for mTLS support.\nUnit tests added for sanitization + mTLS path.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@acastellon/auth"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.3.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/antonio-castellon/module-auth/security/advisories/GHSA-gfj5-979r-92pw"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/antonio-castellon/module-auth/issues/6"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/antonio-castellon/module-auth"
  }, {
    "type" : "WEB",
    "url" : "https://www.npmjs.com/package/@acastellon/auth/v/2.3.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-290" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-18T17:22:47Z",
    "nvd_published_at" : null
  }
}