CVE-2026-4628: Keycloak Auth Bypass Vulnerability

CVE-2026-4628 Overview

A flaw was found in Keycloak. An improper Access Control vulnerability in Keycloak's User-Managed Access (UMA) resource_set endpoint allows attackers with valid credentials to bypass the allowRemoteResourceManagement=false restriction. This occurs due to incomplete enforcement of access control checks on PUT operations to the resource_set endpoint. This issue enables unauthorized modification of protected resources, impacting data integrity.

Critical Impact

Authenticated attackers can bypass access control restrictions to modify protected UMA resources, potentially compromising data integrity across affected Keycloak deployments.

Affected Products

• Keycloak (specific versions to be determined via vendor advisory)

Discovery Timeline

• 2026-03-23 - CVE CVE-2026-4628 published to NVD
• 2026-03-23 - Last updated in NVD database

Technical Details for CVE-2026-4628

Vulnerability Analysis

This vulnerability stems from an Improper Access Control weakness (CWE-284) in Keycloak's User-Managed Access (UMA) implementation. The UMA protocol provides a standardized approach for resource owners to control access to their protected resources. However, the resource_set endpoint fails to properly enforce access restrictions when processing PUT requests.

When administrators configure allowRemoteResourceManagement=false, the intent is to prevent remote clients from modifying resource definitions. However, due to incomplete validation logic, authenticated users can still successfully execute PUT operations against the resource_set endpoint, effectively bypassing this security control. The attack requires network access and valid credentials but does not require user interaction, making it relatively straightforward for authenticated attackers to exploit.

Root Cause

The root cause lies in incomplete enforcement of the allowRemoteResourceManagement configuration flag. While the setting is designed to restrict remote resource management capabilities, the access control checks are not consistently applied across all HTTP methods targeting the resource_set endpoint. Specifically, PUT operations lack the necessary validation to verify whether remote resource management is permitted, creating a bypass condition.

Attack Vector

The attack requires an authenticated user with valid Keycloak credentials. The attacker sends a crafted PUT request to the UMA resource_set endpoint to modify protected resource definitions. Despite the allowRemoteResourceManagement=false configuration being in place, the incomplete access control validation allows the modification to succeed.

The attack flow involves:

1. Attacker authenticates to the Keycloak instance with valid credentials
2. Attacker crafts a PUT request targeting the /auth/realms/{realm}/authz/protection/resource_set/{resource_id} endpoint
3. The request bypasses the allowRemoteResourceManagement check due to incomplete enforcement
4. Resource definitions are modified without proper authorization

For detailed technical information, refer to the Red Hat CVE-2026-4628 Advisory and Red Hat Bug Report #2450240.

Detection Methods for CVE-2026-4628

Indicators of Compromise

• Unexpected PUT requests to the UMA resource_set endpoint from authenticated users
• Unauthorized modifications to UMA resource definitions in Keycloak audit logs
• Changes to protected resource configurations that were not initiated by administrators
• Anomalous access patterns targeting the /auth/realms/{realm}/authz/protection/resource_set/ path

Detection Strategies

• Monitor Keycloak access logs for PUT requests to the resource_set endpoint, especially when allowRemoteResourceManagement is configured as false
• Implement alerting for any modifications to UMA resource definitions outside of approved change windows
• Deploy SentinelOne Singularity to detect suspicious API access patterns and unauthorized resource modifications
• Configure SIEM correlation rules to identify authenticated users making unexpected resource management requests

Monitoring Recommendations

• Enable comprehensive audit logging for all UMA-related endpoints in Keycloak
• Establish baseline patterns for legitimate resource_set modifications to identify anomalous activity
• Implement real-time alerting for configuration changes to protected resources
• Review Keycloak audit trails regularly for signs of access control bypass attempts

How to Mitigate CVE-2026-4628

Immediate Actions Required

• Review the Red Hat CVE-2026-4628 Advisory for vendor-specific patch information
• Audit all UMA resource configurations for unauthorized modifications
• Restrict network access to Keycloak administrative endpoints using firewall rules or network segmentation
• Review and minimize the number of users with credentials that could potentially exploit this vulnerability

Patch Information

Consult the Red Hat Security Advisory for the latest patch releases and upgrade guidance. Organizations should monitor the Red Hat Bug Report #2450240 for updates on the remediation status.

Workarounds

• Implement network-level restrictions to limit access to UMA endpoints from trusted sources only
• Deploy a Web Application Firewall (WAF) to filter and monitor PUT requests to the resource_set endpoint
• Consider disabling UMA functionality entirely if not required for business operations until a patch is available
• Implement additional authentication controls or multi-factor authentication for administrative access

# Example: Restrict access to UMA endpoints via reverse proxy (nginx)
location ~ ^/auth/realms/.*/authz/protection/resource_set {
    # Allow only from trusted internal networks
    allow 10.0.0.0/8;
    allow 192.168.0.0/16;
    deny all;
    
    # Forward to Keycloak
    proxy_pass http://keycloak-backend;
}