CVE-2016-4545 in BIG-IP
Summary
by MITRE
Virtual servers in F5 BIG-IP 11.5.4, when SSL profiles are enabled, allow remote attackers to cause a denial of service (resource consumption and Traffic Management Microkernel restart) via an SSL alert during the handshake.
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Analysis
by VulDB Data Team • 01/06/2019
The vulnerability identified as CVE-2016-4545 affects F5 BIG-IP version 11.5.4 systems that have SSL profiles enabled, presenting a significant denial of service risk that can compromise network infrastructure availability. This issue manifests when remote attackers exploit a flaw in the SSL handshake process by sending specially crafted SSL alert messages, causing the system to consume excessive resources and ultimately restart the Traffic Management Microkernel component. The vulnerability specifically targets the handling of SSL alerts during the initial handshake phase, which is a critical component of secure communication protocols.
The technical root cause of this vulnerability lies in the improper handling of SSL alert messages within the BIG-IP SSL profile implementation. When an SSL alert is received during the handshake process, the system fails to properly validate or sanitize the alert data before processing it, leading to resource exhaustion. This flaw can be categorized under CWE-20, which represents improper input validation, and more specifically aligns with CWE-400, indicating an unchecked resource consumption vulnerability. The Traffic Management Microkernel, which serves as the core component responsible for managing traffic flows and SSL termination in F5 BIG-IP systems, becomes overwhelmed by the malformed alert processing and subsequently restarts, creating a denial of service condition that affects all services relying on the affected system.
The operational impact of CVE-2016-4545 extends beyond simple service disruption, as it can potentially be exploited to create sustained denial of service attacks against critical network infrastructure. Attackers can leverage this vulnerability to repeatedly send SSL alert messages, causing continuous resource exhaustion and system restarts that can persist until manual intervention occurs. The vulnerability affects the availability aspect of the CIA triad and can be mapped to ATT&CK technique T1499.004, which covers network disruption attacks. Organizations using F5 BIG-IP systems in production environments face significant risk from this vulnerability, as it can be exploited remotely without authentication, making it particularly dangerous for systems that are exposed to untrusted networks or internet-facing services.
Mitigation strategies for CVE-2016-4545 should include immediate application of F5's official security patches and updates, which address the SSL alert handling flaw in the Traffic Management Microkernel. Network administrators should also implement monitoring solutions that can detect unusual patterns of SSL alert traffic and resource consumption spikes that may indicate exploitation attempts. Additionally, implementing rate limiting and connection throttling mechanisms for SSL handshake processes can help reduce the impact of potential attacks. The vulnerability highlights the importance of proper input validation and resource management in security-critical components, and organizations should conduct regular security assessments of their network infrastructure to identify similar vulnerabilities in other systems. System administrators should also consider implementing network segmentation and access controls to limit exposure of vulnerable BIG-IP systems to untrusted networks while maintaining necessary connectivity for legitimate operations.