CVE-2018-15326 in BIG-IP APM
Summary
by MITRE
In some situations on BIG-IP APM 14.0.0-14.0.0.2, 13.0.0-13.1.0.7, 12.1.0-12.1.3.5, or 11.6.0-11.6.3.2, the CRLDP Auth access policy agent may treat revoked certificates as valid when the BIG-IP APM system fails to download a new Certificate Revocation List.
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Analysis
by VulDB Data Team • 06/04/2023
The vulnerability described in CVE-2018-15326 represents a critical certificate validation flaw within F5 BIG-IP Access Policy Manager systems that directly impacts the security posture of organizations relying on these platforms for authentication and access control. This issue specifically affects multiple versions of the BIG-IP APM software, spanning from version 11.6.0 through 14.0.0.2, creating a widespread exposure across enterprise environments that utilize F5's application delivery and access management solutions. The flaw resides in the CRLDP Auth access policy agent component, which is responsible for validating certificate revocation status through Certificate Revocation List Distribution Points. When the system fails to download updated Certificate Revocation Lists, the agent incorrectly treats revoked certificates as valid, effectively undermining the fundamental security mechanism designed to prevent access with compromised credentials.
The technical implementation of this vulnerability stems from a failure in the certificate validation process where the BIG-IP APM system maintains a cache of Certificate Revocation Lists but does not properly handle scenarios where the system cannot fetch updated lists from the distribution points. This behavior creates a security blind spot where certificates that have been revoked due to compromise, key leakage, or other security incidents continue to be accepted as valid for authentication purposes. The flaw operates at the policy enforcement level, meaning that even when certificate revocation occurs, the system's access control mechanisms fail to recognize the revocation status, allowing unauthorized access to protected resources. According to CWE-290, this vulnerability maps to authentication bypass through reliance on cached invalid data, while the ATT&CK framework categorizes this under privilege escalation techniques where adversaries can maintain access through compromised credentials that should have been revoked.
The operational impact of this vulnerability extends beyond simple authentication failures to create significant security risks for organizations using F5 BIG-IP APM systems. When revoked certificates continue to be accepted as valid, attackers who have obtained compromised certificates can maintain access to protected applications and systems without detection. This scenario particularly affects environments where certificate-based authentication is used for VPN access, web application security, or other critical access control scenarios. The vulnerability creates a persistent threat vector where security incidents involving certificate compromise can remain undetected for extended periods, potentially allowing attackers to maintain long-term access to sensitive systems. Organizations may experience unauthorized access to critical resources, data exfiltration, and potential lateral movement within their networks, as the system's ability to enforce certificate-based access controls is fundamentally compromised.
Mitigation strategies for CVE-2018-15326 require immediate attention from security administrators and system operators. The primary recommendation involves applying the official F5 security patches and updates released to address this specific vulnerability, as these updates typically include enhanced certificate validation logic and improved handling of CRL download failures. Organizations should implement monitoring procedures to detect when Certificate Revocation Lists fail to download properly and establish alerting mechanisms for such failures. Network administrators should consider implementing additional validation checks outside the affected system to verify certificate status through alternative means, such as direct CRL checking or OCSP validation. The implementation of certificate lifecycle management processes becomes crucial, ensuring that revoked certificates are promptly removed from all systems and that regular audits verify the integrity of certificate validation processes. Additionally, organizations should consider implementing network segmentation and additional access controls to limit the impact of compromised certificates even when the primary validation mechanism fails. These measures align with security best practices outlined in NIST SP 800-57 and ISO/IEC 27001 standards for certificate management and access control, providing a comprehensive approach to mitigating the risk associated with this vulnerability while maintaining operational continuity.