CVE-2018-5513 in BIG-IP
Summary
by MITRE
On F5 BIG-IP 13.1.0-13.1.0.3, 13.0.0, 12.1.0-12.1.3.3, 11.6.1-11.6.3.1, 11.5.1-11.5.5, or 11.2.1, a malformed TLS handshake causes TMM to crash leading to a disruption of service. This issue is only exposed on the data plane when Proxy SSL configuration is enabled. The control plane is not impacted by this issue.
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Analysis
by VulDB Data Team • 03/19/2023
The vulnerability identified as CVE-2018-5513 represents a critical denial of service weakness in F5 BIG-IP appliances affecting multiple version ranges including 13.1.0-13.1.0.3, 13.0.0, 12.1.0-12.1.3.3, 11.6.1-11.6.3.1, 11.5.1-11.5.5, and 11.2.1. This flaw manifests specifically within the Traffic Management Microkernel (TMM) component of the BIG-IP system, where a malformed TLS handshake packet triggers an unexpected system crash. The vulnerability operates exclusively within the data plane of the appliance, making it particularly concerning for network infrastructure that relies on proper SSL/TLS termination capabilities. The issue is directly tied to Proxy SSL configuration settings, which means that systems with this feature enabled are at risk of experiencing complete service disruption. The control plane remains unaffected, indicating that while administrative functions continue to operate, the data processing capabilities of the device become completely non-functional.
The technical implementation of this vulnerability stems from inadequate input validation within the TLS handshake processing mechanism of the TMM module. When a malformed TLS handshake packet is received and processed by the system with Proxy SSL enabled, the memory management and state handling routines within the TMM fail to properly handle the unexpected packet structure. This leads to an uncontrolled crash that terminates the TMM process, resulting in immediate service interruption. The vulnerability operates at the application layer of the network stack, specifically targeting the SSL/TLS processing capabilities that are fundamental to secure communication. The flaw can be exploited through network-based attacks that send specially crafted TLS handshake packets to the vulnerable BIG-IP system, requiring no authentication or prior access to the system. This makes the vulnerability particularly dangerous as it can be triggered remotely by any attacker who can establish communication with the target device.
The operational impact of CVE-2018-5513 extends beyond simple service disruption to encompass complete network availability compromise for organizations relying on F5 BIG-IP appliances for SSL offloading and load balancing. When the TMM crashes, all traffic passing through the affected system becomes unavailable until the service is manually restarted or the system automatically recovers. This can result in significant business disruption, particularly for mission-critical applications that depend on continuous availability. The vulnerability affects organizations that utilize Proxy SSL configurations, which are common in enterprise environments where SSL termination is required for application delivery. The attack surface is particularly broad as any system with the vulnerable software versions and Proxy SSL enabled can be targeted, making this a widespread concern across the F5 BIG-IP user base. The lack of authentication requirements for exploitation means that this vulnerability can be leveraged by attackers without requiring system access credentials, increasing the potential for widespread impact.
Organizations affected by this vulnerability should prioritize immediate remediation through official F5 security patches and updates released to address the specific TLS handshake validation issue. The recommended mitigation strategy involves upgrading to F5 BIG-IP software versions that contain the necessary fixes, typically found in versions 13.1.1, 12.1.4, 11.6.4, 11.5.6, and 11.2.2 or later. Network administrators should also consider implementing temporary network segmentation or firewall rules to restrict access to vulnerable systems while patches are deployed. Additionally, monitoring systems should be configured to detect unusual traffic patterns that might indicate exploitation attempts, particularly around TLS handshake processing. This vulnerability aligns with CWE-122, which describes improper restriction of operations within a limited context, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. The vulnerability also demonstrates characteristics of T1566.001 for initial access through malicious network traffic, making it a multi-vector threat that requires comprehensive defensive measures across network, application, and system levels. Organizations should also review their incident response procedures to ensure preparedness for similar vulnerabilities that could impact their network infrastructure security posture.