CVE-2026-58399
CVE-2026-58399 is a high-severity vulnerability with a CVSS 4.0 base score of 8.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-287.
Key facts
- Severity: High (CVSS 4.0 base score 8.7)
- EPSS exploit prediction: 1% (42nd percentile)
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-287
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-58399?
- @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.
- How severe is CVE-2026-58399?
- CVE-2026-58399 has a CVSS 4.0 base score of 8.7, rated high severity.
- Is CVE-2026-58399 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.
- How do I fix CVE-2026-58399?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
- When was CVE-2026-58399 published?
- CVE-2026-58399 was published on 2026-07-01 and last updated on 2026-07-02.
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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