CVE-2026-2603 is a critical authentication bypass vulnerability discovered in the Red Hat build of Keycloak version 26.2. Keycloak is an open-source identity and access management solution widely used for single sign-on (SSO) and identity federation. The vulnerability specifically affects the SAML endpoint responsible for handling Identity Provider (IdP)-initiated broker logins. In a typical secure setup, Keycloak verifies that the SAML response originates from an enabled and trusted IdP before completing the login process. However, due to missing authentication checks, an attacker can craft and send a valid SAML response from an external IdP—even one that is disabled or not trusted in the Keycloak configuration—and successfully complete the broker login process. This bypasses Keycloak’s security controls, allowing unauthorized access to protected resources. The vulnerability does not require user interaction and can be exploited remotely over the network. The CVSS v3.1 base score is 8.1, indicating high severity, with attack vector network (AV:N), low attack complexity (AC:L), requiring low privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), and high impact on confidentiality and integrity (C:H/I:H/A:N). No public exploits have been reported yet, but the flaw poses a significant risk to organizations relying on Keycloak for federated authentication, especially in environments where IdP-initiated logins are enabled or where multiple IdPs are configured. The vulnerability highlights the importance of strict validation of SAML responses and proper enforcement of IdP enablement status in broker login flows.

The impact of CVE-2026-2603 is substantial for organizations using Keycloak 26.2 for identity federation and SSO. Successful exploitation allows attackers to bypass authentication controls and gain unauthorized access to applications and services protected by Keycloak. This compromises confidentiality by exposing sensitive user data and potentially internal systems. Integrity is also affected as attackers can impersonate legitimate users, perform unauthorized actions, and escalate privileges within the affected environment. Availability is not directly impacted, but the breach could lead to further attacks disrupting services. The vulnerability can be exploited remotely without user interaction, increasing the risk of automated or large-scale attacks. Organizations in sectors such as finance, healthcare, government, and technology that rely on Keycloak for secure authentication are particularly vulnerable. The ability to bypass disabled IdP restrictions also complicates incident response and trust management, potentially allowing attackers to exploit legacy or misconfigured IdPs. Overall, the threat undermines the trust model of federated authentication and could facilitate lateral movement and data breaches.

To mitigate CVE-2026-2603, organizations should immediately upgrade to a fixed version of Red Hat's Keycloak build once available. In the absence of a patch, administrators should disable IdP-initiated broker logins if not strictly required, reducing the attack surface. Review and tighten SAML broker login configurations to ensure only trusted and enabled IdPs are permitted. Implement strict validation of SAML responses, including issuer verification and signature checks, to prevent acceptance of responses from unauthorized IdPs. Employ network-level controls such as IP whitelisting or firewall rules to restrict access to the Keycloak SAML endpoint to known and trusted sources. Monitor authentication logs for unusual broker login activity, especially from unexpected IdPs or IP addresses. Conduct regular audits of IdP configurations to remove or disable unused or legacy IdPs. Consider deploying Web Application Firewalls (WAFs) with custom rules to detect and block anomalous SAML requests. Finally, educate security teams about the vulnerability to ensure rapid detection and response to potential exploitation attempts.