CVE-2018-5542 in BIG-IP
Summary
by MITRE
F5 BIG-IP 13.0.0-13.0.1, 12.1.0-12.1.3.6, or 11.2.1-11.6.3.2 HTTPS health monitors do not validate the identity of the monitored server.
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Analysis
by VulDB Data Team • 04/25/2023
The CVE-2018-5542 vulnerability affects F5 BIG-IP systems running specific versions of the BIG-IP configuration utility, particularly those in the 13.0.0-13.0.1, 12.1.0-12.1.3.6, and 11.2.1-11.6.3.2 release ranges. This flaw resides within the HTTPS health monitoring functionality that administrators use to verify the operational status of backend servers. The vulnerability represents a critical security gap in the system's ability to authenticate server identities during health checks, creating potential pathways for malicious actors to exploit the monitoring infrastructure.
The technical flaw manifests in the HTTPS health monitor implementation where the system fails to properly validate the server certificate presented during the health check process. This validation failure occurs specifically when the BIG-IP system performs HTTPS health checks against monitored endpoints, allowing attackers to potentially present a fraudulent certificate that would still pass the health check validation. The vulnerability stems from inadequate certificate verification mechanisms within the health monitoring framework, which should normally ensure that the certificate presented by the monitored server matches the expected identity of the target system. This weakness falls under the CWE-295 vulnerability category, which specifically addresses improper certificate validation and certificate pinning failures in security implementations.
The operational impact of this vulnerability is significant as it allows for man-in-the-middle attacks against the health monitoring system itself. Attackers could potentially redirect traffic to malicious endpoints that present valid-looking certificates but are controlled by the attacker, causing the BIG-IP system to mark legitimate servers as down while routing traffic to compromised systems. This creates a scenario where the health monitoring system becomes a vector for traffic redirection rather than a tool for ensuring service availability. The vulnerability directly impacts the availability and integrity of the network infrastructure, potentially allowing attackers to disrupt services while maintaining operational stealth. From an attack perspective, this vulnerability aligns with techniques described in the ATT&CK framework under the T1566 tactic for credential harvesting and T1071 for application layer protocol usage, as it enables attackers to manipulate health monitoring systems to achieve their objectives.
Organizations affected by this vulnerability should immediately implement mitigations including applying the vendor-provided security patches, implementing additional certificate validation controls, and potentially reconfiguring health monitoring to use more secure verification methods. The vulnerability represents a fundamental flaw in the BIG-IP system's trust model during health checks, where the system should be validating certificate chains and subject names against expected values. Network administrators should also consider implementing additional monitoring of health check behaviors to detect potential exploitation attempts and ensure that certificate validation is properly enforced throughout the system's configuration. The remediation process should include comprehensive testing of health monitoring configurations to ensure that certificate validation is properly enforced and that the system correctly identifies valid versus invalid server certificates during the health checking process.