CVE-2020-35509 in Keycloak
Summary
by MITRE • 08/23/2022
A flaw was found in keycloak affecting versions 11.0.3 and 12.0.0. An expired certificate would be accepted by the direct-grant authenticator because of missing time stamp validations. The highest threat from this vulnerability is to data confidentiality and integrity.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 06/30/2025
The vulnerability identified as CVE-2020-35509 represents a critical security flaw in the Keycloak identity and access management platform that affects versions 11.0.3 and 12.0.0. This issue resides within the direct-grant authenticator component which is responsible for validating user credentials during authentication processes. The flaw stems from inadequate timestamp validation mechanisms that fail to properly verify certificate expiration dates, creating a significant security gap in the authentication pipeline. According to CWE-295, this vulnerability maps to improper certificate validation practices where the system accepts expired certificates without proper time-based verification, directly violating fundamental security principles of certificate-based authentication.
The technical implementation of this vulnerability occurs within the certificate validation logic of Keycloak's direct-grant authenticator module. When a certificate is presented during authentication, the system should verify that the certificate is currently valid and has not expired based on its not-before and not-after timestamps. However, the missing timestamp validation allows certificates that have exceeded their validity period to be accepted as legitimate authentication credentials. This flaw essentially creates a backdoor where expired certificates can bypass authentication checks, potentially enabling unauthorized access to protected resources and systems that rely on Keycloak for identity management.
The operational impact of this vulnerability extends beyond simple authentication bypass scenarios and poses serious threats to data confidentiality and integrity as noted in the original description. Attackers who can obtain or generate expired certificates could leverage this weakness to impersonate legitimate users or gain unauthorized access to sensitive systems and data. The vulnerability particularly affects environments where certificate-based authentication is heavily relied upon, potentially allowing attackers to establish persistent access to critical infrastructure. Organizations using Keycloak for managing user identities and access controls face significant risk of data breaches, privilege escalation, and unauthorized system modifications. This vulnerability directly aligns with ATT&CK technique T1550.001 for valid accounts and T1078.004 for valid accounts, as it enables unauthorized access through compromised or misconfigured authentication mechanisms.
Mitigation strategies for CVE-2020-35509 should prioritize immediate patching of affected Keycloak versions to the latest stable releases that contain proper timestamp validation fixes. Organizations should implement comprehensive certificate management policies that include regular certificate lifecycle monitoring and automated expiration notifications. Network segmentation and additional authentication layers should be deployed to reduce the attack surface and limit the impact of potential exploitation. Security teams should conduct thorough audits of certificate usage within Keycloak environments and implement monitoring solutions that can detect anomalous authentication patterns. Additionally, organizations should review their overall identity and access management practices to ensure that certificate-based authentication is properly configured with appropriate validation mechanisms that prevent the acceptance of expired credentials. The vulnerability demonstrates the critical importance of proper certificate validation in security infrastructure and highlights the need for robust time-based validation checks in all authentication systems.