What’s Vulnerable › Vulnerabilities

CVE-2026-58399: @acastellon/auth has an authentication bypass via spoofable headers in validateToken()

• Severity: high (CVSS 8.7 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.0% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-01 · updated 2026-10-25
• Weakness: CWE-287

Description

@acastellon/auth is an authentication control system for microservices. Versions prior to 2.3.0 appear 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. A fix has been implemented in v2.3.0.

Affected products

• antonio-castellon module-auth: before 2.3.0

References

• https://github.com/antonio-castellon/module-auth/issues/6
• https://github.com/antonio-castellon/module-auth/security/advisories/GHSA-gfj5-979r-92pw
• https://www.npmjs.com/package/@acastellon/auth/v/2.3.0

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