CVE-2026-16093
MediumCVSS 5.4Exploitation Probability (EPSS)
Low risk9th percentile - higher than 9% of all known CVEs
Summary
A flaw in Keycloak's Client Policies mechanism allows bypassing the requirement for signed JWT assertions. An attacker with valid client credentials can provide a fake, unsigned assertion header, tricking the system into thinking policy requirements are met.
Risk Assessment
The organization is at risk of an attacker authenticating using simpler methods (e.g., client secret) even when the administrator mandated more secure signed assertions, potentially leading to unauthorized access to protected resources.
Recommendation
Immediately update Keycloak to a patched version. Until then, consider additional access control mechanisms such as monitoring for unusual authentication attempts.
Other vulnerabilities in Keycloak
See all- CVE-2026-19608Medium
A flaw was found in the group policy provider of Keycloak authorization services, which is used to manage fine-grained access control to resources. The issue occurs when the system evaluates group-based policies using tokens that only contain group names rather than full paths. If two groups in different parts of the organization share the same name, a user in the unauthorized group can be mistaken for a member of the authorized group. This can allow a user to gain unauthorized access to protected resources they should not be able to reach.
- CVE-2026-0707Medium
A flaw was found in Keycloak regarding the authorization header parser. This parser is overly permissive regarding the formatting of the 'Bearer' authentication scheme, accepting non-standard characters as separators and tolerating case variations that deviate from RFC 6750 specifications.
- CVE-2017-12159High
It was found that the cookie used for CSRF prevention in Keycloak was not unique to each session. An attacker could use this flaw to gain access to an authenticated user session, leading to possible information disclosure or further attacks.
- CVE-2026-79652Medium
A flaw was found in the JWT Bearer authorization grant implementation within the keycloak-services component of Red Hat Build of Keycloak. The grant fails to check if a client requires user consent before issuing a token. This allows an authenticated attacker with valid client credentials and a trusted identity provider assertion to bypass the consent requirement and obtain unauthorized access to a user account at a consent-gated client.
- CVE-2026-15571High
Keycloak contains a vulnerability in the legacy account-linking endpoint, where the protection mechanism based on a hash can be predicted by a malicious OIDC client. An attacker can forge a linking URL to connect the victim's account to an attacker-controlled external identity, leading to full account takeover.
- CVE-2026-18967Medium
In the SAML broker component of Keycloak, when configured with IdP-Initiated flow, the OneTimeUse condition in SAML assertions is not enforced. This allows an attacker who captures a valid, unused assertion to replay it multiple times, potentially hijacking a user's session.
- CVE-2026-16442High
A flaw in the SAML broker component of Keycloak, used for identity federation and user authentication. The IdP-initiated Single Sign-On endpoint fails to check if a provider is restricted to account linking only, allowing an attacker with control over a linked upstream identity to bypass login restrictions and gain full access to a local user account.
- CVE-2026-15572High
A flaw in Keycloak's Dynamic Client Registration (DCR) security policy management. The "Allowed Protocol Mapper Types" policy fails to re-validate the mapper type during a client update if the mapper's configuration remains unchanged. An attacker with client registration privileges can register an allowed mapper type with malicious configuration and then swap it for a restricted, high-privilege mapper type, gaining full administrative access to the realm.
- CVE-2026-16102High
A flaw in the Dynamic Client Registration (DCR) component of Keycloak. The default DCR policy fails to properly validate the claim path for User Property mappers, allowing them to write values to sensitive internal claim locations. An attacker with a standard user account and a limited Initial Access Token can forge administrative roles in their access token, leading to takeover of other clients, theft of confidential secrets, and potential full administrative control over the realm.
- CVE-2026-16100Medium
A flaw was found in the user-event metrics recording of Keycloak. When metrics are enabled, the system records raw error messages from failed account operations as Prometheus metric labels. Because these error messages can include user-supplied input like nonexistent client IDs, an authenticated user can create a massive number of unique metric entries, eventually exhausting system memory and causing the service to crash or become unavailable.
Original NVD description (English source)
Keycloak provides a mechanism called Client Policies to enforce security requirements on clients, such as requiring them to use signed JWTs for authentication. A flaw was discovered where this enforcement can be bypassed. An attacker with valid client credentials can provide a fake, unsigned assertion header that tricks the system into thinking the policy requirements have been met. This allows the attacker to authenticate using simpler methods like a client secret even when the administrator has mandated more secure, signed assertions.