User Impersonation Affecting @acastellon/auth package, versions <2.3.0
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-ACASTELLONAUTH-17817129
- published4 Jul 2026
- disclosed18 Jun 2026
- creditUnknown
Introduced: 18 Jun 2026
NewCVE-2026-58399 (opens in a new tab)How to fix?
Upgrade @acastellon/auth to version 2.3.0 or higher.
Overview
@acastellon/auth is an Authorization Filtering for NodeJS Express Application (NTLM + LDAP + JWT + AWS Cognito + Azure AD/Entra ID + OIDC providers + SAML + env var secrets)
Affected versions of this package are vulnerable to User Impersonation via the validateToken process. An attacker can gain unauthorized access to protected routes and potentially escalate privileges by sending crafted HTTP requests with spoofed auth-user and Host headers, causing the middleware to bypass token validation before standard authentication checks are performed. This is only exploitable if downstream services trust the auth-user or is-* headers provided by the client.