A flaw was found in Keycloak. An unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with an excessively long scope parameter to the OpenID Connect (OIDC) token endpoint. This leads to high resource consumption and prolonged processing times, ultimately resulting in a Denial of Service (DoS) for the Keycloak server.

Keycloak installed on the remote host is 26.2.x prior to 26.2.15, 26.4.x prior to  26.4.11, 26.5.x prior to 26.5.7 are affected by multiple vulnerabilities:

  - A privilege escalation flaw exists due to improper isolation in the SingleUseObjectProvider. An     unauthenticated, remote attacker can forge authorization codes and potentially obtain admin-capable     access tokens. (CVE-2026-4282)

  - A denial of service flaw exists in the OpenID Connect token endpoint. An unauthenticated, remote     attacker can exhaust server CPU and memory by sending an excessively long scope parameter.
    (CVE-2026-4634)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - A flaw was found in Keycloak. An unauthenticated attacker can exploit this vulnerability by sending a
    specially crafted POST request with an excessively long scope parameter to the OpenID Connect (OIDC) token
    endpoint. This leads to high resource consumption and prolonged processing times, ultimately resulting in
    a Denial of Service (DoS) for the Keycloak server. (CVE-2026-4634)

ID	Name	Product	Family	Type	Severity
330085	Keycloak 26.2 < 26.2.15 / 26.4 < 26.4.11 / 26.5 < 26.5.7 Multiple Vulnerabilities	Nessus	Misc.	Local	high
439847	SCA: security update for org.keycloak:keycloak-services (GHSA-h4wv-g838-66g3)	Tenable Cloud Security	SCA Checks	Local	high
439847	SCA: security update for org.keycloak:keycloak-services (GHSA-h4wv-g838-66g3)	Tenable Self-Hosted Container Security	SCA Checks	Local	high

Detections

Analytics

CVE-2026-4634

high

Tenable Plugins

high

high

high