CVE-2019-3875 in KeyCloak
Summary
by MITRE
A vulnerability was found in keycloak before 6.0.2. The X.509 authenticator supports the verification of client certificates through the CRL, where the CRL list can be obtained from the URL provided in the certificate itself (CDP) or through the separately configured path. The CRL are often available over the network through unsecured protocols ('http' or 'ldap') and hence the caller should verify the signature and possibly the certification path. Keycloak currently doesn't validate signatures on CRL, which can result in a possibility of various attacks like man-in-the-middle.
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Analysis
by VulDB Data Team • 10/05/2023
The vulnerability identified as CVE-2019-3875 resides within the Keycloak identity and access management platform, specifically affecting versions prior to 6.0.2. This flaw manifests in the X.509 authenticator component which is responsible for verifying client certificates through Certificate Revocation Lists. The vulnerability stems from insufficient validation of Certificate Revocation Lists, creating a significant security gap that could be exploited by malicious actors. The X.509 authenticator supports verification of client certificates through CRL mechanisms, where CRL lists can be obtained from URLs specified within the certificate itself through the Certificate Distribution Point (CDP) extension or from separately configured paths. This functionality is designed to maintain certificate validity by checking if certificates have been revoked, but the implementation fails to properly validate the cryptographic signatures on these CRLs.
The technical flaw represents a critical weakness in the certificate validation process where Keycloak does not perform signature validation on Certificate Revocation Lists. This omission means that the system accepts CRLs without verifying their authenticity or integrity, creating a pathway for attackers to inject malicious CRL data. The vulnerability becomes particularly dangerous because CRLs are often distributed over unsecured protocols such as HTTP or LDAP, making them susceptible to man-in-the-middle attacks. When CRLs are obtained through these insecure channels without signature verification, attackers can potentially substitute legitimate CRLs with forged ones that contain revoked certificates for trusted entities. This weakness directly violates security best practices and industry standards, as proper certificate validation requires signature verification to ensure data integrity and authenticity.
The operational impact of this vulnerability is severe and multifaceted, potentially enabling various attack vectors that could compromise the entire authentication infrastructure. An attacker positioned in a man-in-the-middle position could intercept CRL requests and replace them with malicious CRLs that revoke legitimate certificates or fail to revoke compromised ones. This could result in unauthorized access to systems, certificate bypass attacks, or complete disruption of the authentication service. The vulnerability affects the core security assurances provided by the X.509 certificate infrastructure, potentially allowing attackers to authenticate as legitimate users or systems without proper authorization. The impact extends beyond simple authentication bypasses to include potential privilege escalation and data compromise scenarios, particularly in environments where certificate-based authentication is heavily relied upon for security controls.
This vulnerability aligns with CWE-330, which addresses insufficient entropy in a cryptographic algorithm, and represents a failure in proper cryptographic validation as outlined in CWE-327, which deals with use of a broken or risky cryptographic algorithm. From an ATT&CK perspective, this weakness maps to T1552.001 (Credentials in Files) and T1071.004 (Application Layer Protocol: DNS) as attackers could manipulate certificate files or network communications to exploit the vulnerability. The recommended mitigations include upgrading to Keycloak version 6.0.2 or later where proper CRL signature validation has been implemented, configuring secure transport protocols for CRL distribution such as HTTPS or LDAPS, and implementing proper certificate validation policies that enforce signature verification. Organizations should also consider implementing network monitoring to detect suspicious CRL traffic patterns and establish certificate pinning mechanisms where appropriate. Additionally, security teams should review their certificate management practices and ensure that all certificate validation processes include proper signature verification steps to prevent similar vulnerabilities in other components of their security infrastructure.