CVE-2026-4366: Keycloak Information Disclosure Flaw

CVE-2026-4366 Overview

A Server-Side Request Forgery (SSRF) vulnerability has been identified in Keycloak, a widely-used open-source identity and access management solution. The flaw occurs when Keycloak improperly follows HTTP redirects while processing certain client configuration requests. This behavior enables attackers to manipulate the server into making unintended requests to internal or restricted resources, potentially exposing sensitive internal services such as cloud metadata endpoints.

Critical Impact

Attackers can leverage this SSRF vulnerability to access internal network resources, retrieve cloud instance metadata, and map internal infrastructure—potentially leading to further attacks including privilege escalation and data exfiltration.

Affected Products

• Keycloak (specific affected versions to be confirmed via vendor advisory)

Discovery Timeline

• 2026-03-18 - CVE-2026-4366 published to NVD
• 2026-03-18 - Last updated in NVD database

Technical Details for CVE-2026-4366

Vulnerability Analysis

This vulnerability is classified as CWE-918 (Server-Side Request Forgery). The core issue lies in Keycloak's handling of HTTP redirects during client configuration request processing. When the server receives certain configuration requests, it follows HTTP redirects without proper validation of the destination URL, allowing attackers to redirect requests to arbitrary internal or external endpoints.

The network-accessible nature of this vulnerability means attackers can exploit it remotely without authentication. While the vulnerability does not directly allow data modification or cause service disruption, it enables unauthorized read access to internal resources that should not be externally accessible. The scope is changed, meaning the vulnerability in Keycloak can affect resources beyond its own security boundary.

Root Cause

The root cause is improper validation of redirect destinations when Keycloak processes client configuration requests. The application fails to implement adequate URL validation and allowlist controls before following HTTP redirects, trusting the redirect location without verifying whether it points to a safe, authorized destination.

Attack Vector

An attacker can exploit this vulnerability by crafting malicious client configuration requests that trigger Keycloak to follow redirects to internal resources. The attack flow typically involves:

1. The attacker identifies an endpoint in Keycloak that processes client configuration and follows redirects
2. A crafted request is submitted with a redirect pointing to an internal resource (e.g., http://169.254.169.254/latest/meta-data/ for AWS metadata)
3. Keycloak follows the redirect and retrieves the internal resource content
4. The response or error messages may leak information about the internal resource to the attacker

This technique can be used to access cloud provider metadata endpoints, internal APIs, or other network services not intended to be externally accessible. The information disclosed could include cloud credentials, internal service configurations, or details about the internal network topology.

Detection Methods for CVE-2026-4366

Indicators of Compromise

• Unusual outbound requests from Keycloak servers to internal IP ranges (e.g., 10.x.x.x, 172.16.x.x, 192.168.x.x)
• Requests targeting cloud metadata endpoints (169.254.169.254)
• Unexpected HTTP redirects in Keycloak access logs during client configuration operations
• Anomalous network traffic patterns from the Keycloak application server

Detection Strategies

• Monitor Keycloak application logs for client configuration requests with suspicious redirect URLs
• Implement network-level monitoring to detect requests from Keycloak to internal-only services
• Deploy Web Application Firewall (WAF) rules to inspect and block SSRF patterns in requests
• Analyze outbound connection attempts from Keycloak servers for unauthorized destinations

Monitoring Recommendations

• Enable detailed logging for all client configuration request processing in Keycloak
• Set up alerts for any connections from Keycloak to RFC 1918 private address spaces
• Monitor DNS queries from Keycloak servers for internal hostname resolution attempts
• Implement egress filtering and log all blocked outbound connection attempts

How to Mitigate CVE-2026-4366

Immediate Actions Required

• Review and apply vendor patches as they become available from Red Hat and Keycloak
• Implement network segmentation to restrict Keycloak's ability to reach internal services
• Configure egress firewall rules to limit outbound connections from Keycloak servers
• Deploy WAF rules to detect and block SSRF attack patterns

Patch Information

Red Hat has acknowledged this vulnerability. For the latest patch information and remediation guidance, refer to the Red Hat CVE-2026-4366 Advisory. Additional technical details are available in Red Hat Bugzilla Report #2448543.

Organizations should monitor Red Hat's security advisories for official patches and apply them as soon as they become available.

Workarounds

• Implement strict egress filtering on Keycloak servers to prevent connections to internal networks
• Use network policies to block access to cloud metadata endpoints (169.254.169.254)
• Deploy a proxy or gateway that validates and restricts outbound URLs before Keycloak can follow redirects
• Consider disabling or restricting client configuration endpoints if not required for your deployment

# Example: Block cloud metadata endpoint access using iptables
iptables -A OUTPUT -d 169.254.169.254 -j DROP

# Example: Restrict outbound connections to approved destinations only
iptables -A OUTPUT -m owner --uid-owner keycloak -j REJECT
iptables -A OUTPUT -m owner --uid-owner keycloak -d approved-endpoint.example.com -j ACCEPT