Janssen Auth Server EUVD-2026-44969

Exploitation requires two conditions to be simultaneously true: the target Janssen deployment must accept JWE-wrapped JAR request objects at its OIDC authorization endpoint (this is a protocol feature, not the default for all deployments - verify whether the server is configured to accept the 'request' or 'request_uri' parameter with JWE content), and the attacker must be able to construct a syntactically valid JWE token encrypted to the server's RSA public key (typically obtainable from the server's JWKS endpoint at no privilege). The forceSignedRequestObject=true bypass specifically affects deployments that believe this flag enforces signed request object integrity. Limiting factors include: the attacker cannot trivially forge JWE without the server's public key (though public JWKS endpoints eliminate this barrier), JWE request object support may not be enabled by default, and the practical impact is confined to manipulation of authorization request parameters - not direct credential theft or full authentication bypass. The CVSS PR:N is consistent with the authorization endpoint being publicly accessible.

The CVSS 3.1 base score of 5.3 (Medium) with vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N captures a network-reachable, unauthenticated, zero-complexity attack surface - a combination that is concerning for an IAM platform where authorization integrity is foundational. However, the integrity impact is rated Low, and there is no confidentiality or availability impact, reflecting the bounded consequence of parameter manipulation rather than authentication bypass. No EPSS data was provided, so probabilistic exploitation likelihood cannot be quantified from this dataset. The vulnerability is not in CISA KEV, and no public proof-of-concept exploit code has been identified, suggesting it has not seen mass exploitation. Real-world risk is further constrained by deployment conditions: the attacker must be able to construct a JWE encrypted to the server's public key (the JWKS endpoint typically makes this feasible), and the deployment must accept JAR-style JWE request objects (not universally enabled). Organizations with forceSignedRequestObject=true who believed they had a stronger security posture are the primary risk group, as that configuration was specifically bypassable. Overall this is a genuine but targeted-risk finding rather than a mass-exploitation priority.

An unauthenticated attacker retrieves the Janssen server's RSA public key from its JWKS endpoint, encrypts a crafted plain JSON authorization request payload using RSA-OAEP into a valid JWE token, and submits it to the /authorize endpoint as a request object parameter. The server decrypts the JWE, finds no nested signed JWT but proceeds due to the null-check gap, and processes the attacker-supplied authorization parameters without signature verification - enabling manipulation of claims such as redirect_uri, scope, or client_id. No public proof-of-concept code has been identified at time of analysis.