EUVD-2026-41013
GHSA-gfj5-979r-92pw
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Fully remote header spoofing with no auth or interaction gives AV:N/AC:L/PR:N/UI:N; the core impact is forged identity/trust so I:H, with C:N/A:N per the reported scope.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
2Blast Radius
ecosystem impact- 3 npm packages depend on @acastellon/auth (2 direct, 1 indirect)
Ecosystem-wide dependent count for version 2.3.0.
DescriptionCVE.org
@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.
AnalysisAI
Authentication bypass in @acastellon/auth (npm package, aka antonio-castellon/module-auth) before 2.3.0 lets a remote unauthenticated attacker impersonate a trusted internal service by sending spoofed 'auth-user' and 'Host' request headers. The validateToken() middleware short-circuits its own token check when auth-user equals 'service-brother' and the Host header starts with the configured hostname - both fully client-controllable - so an attacker skips legacy/JWT/OIDC validation entirely. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitable when the target application uses @acastellon/auth's validateToken() middleware, which contains the service-to-service bypass for auth-user: service-brother gated on req.get('host').startsWith(getHostName()). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The provided CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N) is internally consistent with the description: fully remote, low complexity, no privileges, no user interaction, high integrity impact (identity/trust forgery) and no confidentiality or availability impact as scored by the reporter. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker who can reach a microservice protected by this middleware sends an HTTP request with the header auth-user: service-brother and a Host header beginning with the service's configured hostname; validateToken() takes the trust fast-path and authorizes the request without any token, granting the attacker the privileges of the internal 'service-brother' identity. No POC is publicly identified, but the attack requires only header manipulation with tools like curl, so complexity is low. |
| Remediation | Vendor-released patch: 2.3.0 - upgrade the dependency to @acastellon/auth 2.3.0 or later (npm install @acastellon/auth@^2.3.0, then rebuild and redeploy affected microservices) as the primary fix, per advisory GHSA-gfj5-979r-92pw (https://github.com/antonio-castellon/module-auth/security/advisories/GHSA-gfj5-979r-92pw). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
24 hours: Inventory all applications and services using @acastellon/auth npm package and document versions in use; assess production exposure. …
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Same weakness CWE-287 – Improper Authentication
View allSame technique Authentication Bypass
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External POC / Exploit Code
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