CVE-2026-58399
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · unedited@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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThe @acastellon/auth middleware prior to v2.3.0 contains an authentication bypass in validateToken() where a service-to-service bypass check compares the client-controlled auth-user header (set to 'service-brother') against a host header that can be spoofed to start with the server's hostname. Since both values are attacker-influential, unauthenticated remote attackers can bypass token validation entirely by sending crafted HTTP headers.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- Authentication
- X
- User interaction
- None
- Scope
- X
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
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed version of @acastellon/authRun 'npm list @acastellon/auth' or inspect your package.json dependencies to identify the exact version number installedAffected if The installed version is lower than v2.3.0 (e.g., v2.2.9, v2.2.0, v2.1.0, etc.)
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Locate the validateToken function usageSearch your codebase for calls to validateToken() from the @acastellon/auth module, typically found in route handlers or middleware configuration filesAffected if Your application uses validateToken() from this package for authentication protection
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Identify if service-to-service bypass is enabledInspect your environment configuration or auth setup code to determine whether the service-to-service bypass logic is active - look for references to 'service-brother' or similar bypass patterns in your auth configurationAffected if The service-to-service bypass mechanism is enabled in your authentication flow
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Review HTTP header handlingExamine your application logs or network traces for incoming requests that include custom auth-user headers or manipulated Host headers, particularly from external sourcesAffected if Your application accepts and processes auth-user or Host headers from untrusted sources without validation
You are affected if your installed @acastellon/auth version is prior to v2.3.0 AND your application uses validateToken() with the service-to-service bypass logic enabled, allowing attackers to inject crafted headers to bypass authentication.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade @acastellon/auth to v2.3.0 or later which contains the fix. Alternatively, temporarily disable the service-to-service bypass logic if upgrade is not immediately feasible.
v2.3.0
- Locate the @acastellon/auth package in your project's package.json file
- Update the version specification for @acastellon/auth to "2.3.0" or use the semver range "^2.3.0" or ">=2.3.0"
- Run "npm install" or "npm update" to install the fixed version
- Verify the installed version by running "npm list @acastellon/auth"
- Test your application's authentication flow to confirm the bypass is mitigated
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-58399 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-58399 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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