CVE-2026-9803

Published May 28, 2026

Last updated a day ago

CVSS medium 5.3

Overview

Description
A flaw was found in Keycloak's ClientRegistrationAuth component. A remote unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with a malformed 'Authorization: Bearer' header to any client registration endpoint. This can lead to an ArrayIndexOutOfBoundsException, causing the server to return an HTTP 500 error and resulting in a Denial of Service (DoS) for the affected service.
Source
secalert@redhat.com
NVD status
Analyzed
Products
build_of_keycloak

Risk scores

CVSS 3.1

Type
Secondary
Base score
5.3
Impact score
1.4
Exploitability score
3.9
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Severity
MEDIUM

Weaknesses

secalert@redhat.com
CWE-125

Social media

Hype score
Not currently trending

Configurations

Related CVEs

  1. A flaw was found in Keycloak. When revokeRefreshToken=true is enabled and persistent session storage is in use, a server restart can reset internal timing mechanisms. This allows a remote attacker, who has previously captured a user's refresh token, to replay that token even after it has been revoked. Successful exploitation grants the attacker unauthorized access to the victim's account, potentially leading to information disclosure or privilege escalation.•CVE-2026-9802
  2. A flaw was found in Keycloak. A remote attacker with high privileges, such as a realm administrator configuring a malicious Lightweight Directory Access Protocol (LDAP) server or an attacker compromising an upstream LDAP server, could exploit this vulnerability. By sending a malformed LDAP password policy response during a password authentication request, the attacker can trigger an OutOfMemoryError. This causes the Keycloak Java Virtual Machine (JVM) to terminate, leading to a denial of service (DoS) for all realms on the affected node.•CVE-2026-9801
  3. A flaw was found in Keycloak, an open-source identity and access management solution. When a user account is temporarily locked due to repeated failed login attempts, an attacker with valid client credentials can exploit the Client-Initiated Backchannel Authentication (CIBA) flow to bypass this brute-force protection. This allows continued authentication attempts and token issuance even when the account should be locked, potentially enabling further unauthorized access attempts.•CVE-2026-9798
  4. A flaw was found in Keycloak. An authenticated administrator with the `manage-clients` role can exploit a Time-of-check to time-of-use (TOCTOU) vulnerability in the name-based admin role checks. This allows the attacker to escalate their privileges to `realm-admin` for all users within the realm, granting them extensive control over the system. The composite role relationship persists even after the attacker's own permissions are revoked and across system reboots.•CVE-2026-9796
  5. A flaw was found in Keycloak's Fine-Grained Admin Permissions (FGAPv2) feature. An administrator with limited client management permissions can exploit this vulnerability to assign any realm role, including highly privileged roles, to a client's scope mapping. This bypasses intended security controls, allowing the injected role to be projected into a user's authentication token when they access the modified client. This could lead to unauthorized privilege escalation within the Keycloak realm.•CVE-2026-9795

References

Sources include official advisories and independent security research.