CVE-2026-96446 in Keycloak Single Sign-On
Summary
by MITRE • 09/23/2026
A flaw was found in the Pushed Authorization Request PAR implementation of Keycloak. The issue occurs when the silent authentication path prompt=none is used, which allows the authorization process to skip certain steps if a user is already logged in. Due to this bypass, the security rule that ensures a pushed request URI is used only once is not enforced. An attacker could potentially reuse a request URI to obtain multiple authorization codes for a user who is already signed in, violating security standards like FAPI-2.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified within Keycloak’s Pushed Authorization Request implementation represents a critical deviation from expected security protocols during the silent authentication flow. Specifically, when the prompt=none parameter is utilized, which signals to the authorization server that no user interaction should be required and allows for automatic session validation if a valid login exists, the system fails to enforce strict one-time use constraints on pushed request URIs. This architectural flaw creates an opportunity for attackers to exploit the stateless nature of certain silent authentication checks by reusing previously issued request identifiers. In standard OAuth 2.0 flows involving Pushed Authorization Requests, it is imperative that each unique URI generated via the push endpoint can only be consumed once to prevent replay attacks and ensure transaction integrity. However, in this specific scenario, the logic governing the reuse of these URIs does not properly invalidate them after a single successful authentication event when operating under silent conditions.
From an operational perspective, this flaw allows an attacker who has obtained or intercepted a pushed request URI to repeatedly submit it against the authorization endpoint while a target user maintains an active session in their browser. Each submission can result in the generation of a new authorization code tied to that same underlying session and identity. This capability effectively bypasses security mechanisms designed to limit the scope and frequency of authentication exchanges, leading to potential account takeover scenarios or unauthorized access if subsequent steps in the OAuth flow are manipulated by an adversary with control over the client application side. The ability to generate multiple valid tokens from a single pushed request undermines the principle of non-repudiation and integrity within the authorization framework, as it allows for indefinite expansion of granted permissions without additional user consent or explicit re-authentication events that would normally trigger such protections.
This issue directly violates requirements outlined in Financial-grade API Security Profile version 2, commonly referred to as FAPI-2, which mandates strict enforcement mechanisms to prevent replay attacks and ensure the uniqueness of authorization requests. The failure to enforce single-use constraints on pushed request URIs during silent authentication paths constitutes a significant compliance gap for organizations relying on Keycloak for high-assurance financial or sensitive data integrations. Furthermore, this vulnerability aligns with CWE-294, which describes Improper Authentication Bypass Using an Alternate Path or Channel, as the attacker exploits a specific code path (silent auth) to bypass standard security controls intended for interactive flows. It also relates to CWE-352 regarding Cross-Site Request Forgery if the reused URI can be leveraged in conjunction with other vectors to perform actions on behalf of the authenticated user without their knowledge.
To mitigate this risk, immediate updates to Keycloak are required to ensure that pushed request URIs are invalidated immediately upon first use, regardless of whether the authentication occurred via an interactive or silent path. Administrators should monitor for unusual patterns in authorization code generation and implement rate limiting on the token endpoint to detect potential abuse stemming from repeated requests using similar identifiers. Additionally, enforcing strict validation checks that verify the uniqueness and expiration status of pushed request URIs before processing any subsequent steps is essential. Until patched, organizations may consider disabling silent authentication flows where feasible or implementing additional client-side safeguards such as state parameter verification and nonce binding to reduce the impact of potential replay attacks. Regular auditing of OAuth logs for anomalies in URI reuse patterns can also aid in early detection of exploitation attempts targeting this specific implementation flaw.