CVE-2026-4366 in Keycloak
Summary
by MITRE • 03/18/2026
A flaw was identified in Keycloak, an identity and access management solution, where it improperly follows HTTP redirects when processing certain client configuration requests. This behavior allows an attacker to trick the server into making unintended requests to internal or restricted resources. As a result, sensitive internal services such as cloud metadata endpoints could be accessed. This issue may lead to information disclosure and enable attackers to map internal network infrastructure.
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Analysis
by VulDB Data Team • 03/22/2026
The vulnerability identified in Keycloak under CVE-2026-4366 represents a critical security flaw in the identity and access management solution that directly impacts how the system handles HTTP redirect responses during client configuration processing. This issue falls under the category of insecure redirect handling, which is classified as CWE-601 in the Common Weakness Enumeration catalog and aligns with ATT&CK technique T1071.004 for application layer protocol tunneling. The flaw exists in the server-side processing logic that fails to properly validate or sanitize redirect URLs, creating a pathway for malicious actors to manipulate the redirect behavior.
The technical implementation of this vulnerability stems from Keycloak's failure to implement proper URL validation when processing redirect configurations submitted by clients. When the server receives a client configuration request containing redirect URLs, it does not adequately verify that these URLs adhere to expected patterns or originate from trusted sources. This improper validation allows attackers to craft malicious redirect URLs that point to internal network resources such as cloud metadata services, internal APIs, or other sensitive endpoints that should remain isolated from external access. The vulnerability is particularly concerning because it operates at the application layer where authentication and authorization controls are typically enforced.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables comprehensive internal network reconnaissance and mapping capabilities for attackers. By leveraging the improper redirect handling, malicious actors can systematically probe internal services that are normally protected by network segmentation and access controls. This reconnaissance capability provides attackers with detailed knowledge of internal infrastructure, including service endpoints, network topology, and potentially sensitive system configurations. The vulnerability can be exploited to access cloud metadata endpoints which often contain sensitive information such as instance IDs, network configurations, and access credentials that can further compound the security impact.
Security mitigation strategies for this vulnerability must address both the immediate technical flaw and broader architectural considerations. Organizations should implement strict URL validation mechanisms that ensure redirect targets are either explicitly whitelisted or conform to predetermined patterns that exclude internal network addresses. The solution should incorporate proper input sanitization and URL parsing to prevent attackers from crafting malicious redirect chains that could lead to information disclosure or further exploitation. Additionally, network segmentation controls and firewall rules should be enforced to limit access to internal services from the Keycloak server, regardless of redirect behavior. Regular security assessments and penetration testing should include validation of redirect handling mechanisms to prevent similar vulnerabilities from being introduced in future deployments. The implementation of these controls aligns with security frameworks such as NIST SP 800-53 and ISO 27001 requirements for secure application development and network protection.