CVE-2017-6136 in BIG-IP Virtual Server
Summary
by MITRE
In F5 BIG-IP LTM, AAM, AFM, Analytics, APM, ASM, DNS, GTM, Link Controller, PEM and WebSafe software version 13.0.0 and 12.0.0 - 12.1.2, undisclosed traffic patterns sent to BIG-IP virtual servers, with the TCP Fast Open and Tail Loss Probe options enabled in the associated TCP profile, may cause a disruption of service to the Traffic Management Microkernel (TMM).
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Analysis
by VulDB Data Team • 01/18/2023
The vulnerability described in CVE-2017-6136 represents a significant denial of service weakness within F5 BIG-IP systems that affects multiple modules including Local Traffic Manager AAM AFM Analytics APM ASM DNS GTM Link Controller PEM and WebSafe. This flaw specifically manifests when certain traffic patterns are processed through virtual servers configured with TCP Fast Open and Tail Loss Probe options enabled in their TCP profiles. The vulnerability operates at the network protocol level and demonstrates how seemingly benign TCP stack configurations can create exploitable conditions that disrupt critical infrastructure services.
The technical mechanism behind this vulnerability involves the interaction between TCP Fast Open and Tail Loss Probe features within the Traffic Management Microkernel (TMM) component of F5 BIG-IP appliances. When specific traffic patterns are received by virtual servers with these TCP profile options enabled, the TMM process becomes unstable and may crash or become unresponsive. This occurs because the combination of these TCP options creates unexpected state transitions in the kernel's handling of network connections. The vulnerability is particularly concerning because it affects the core traffic management functionality of the appliance, potentially causing widespread service disruption across multiple network services simultaneously.
The operational impact of CVE-2017-6136 extends beyond simple service disruption as it can affect the availability of critical network infrastructure components. Organizations relying on F5 BIG-IP appliances for load balancing application delivery and security services face potential downtime that could span from minutes to hours depending on the scale of affected virtual servers. The vulnerability's exploitation requires specific conditions including the presence of particular TCP profile configurations and the receipt of specific traffic patterns, making it somewhat targeted but still dangerous in production environments where network traffic can be unpredictable. This vulnerability directly relates to CWE-119 which addresses memory access violations and improper access to resources.
Network administrators and security teams should consider this vulnerability in the context of the MITRE ATT&CK framework where it could be categorized under T1499 which covers network denial of service attacks. The vulnerability affects multiple F5 BIG-IP modules and represents a critical weakness in the appliance's TCP stack implementation. Organizations should implement immediate mitigations including disabling TCP Fast Open and Tail Loss Probe options in TCP profiles for affected virtual servers, or upgrading to patched versions of the F5 BIG-IP software. The vulnerability demonstrates how advanced TCP features can create unexpected security implications when combined with specific traffic patterns.
Mitigation strategies should focus on both immediate remediation and long-term architectural considerations. Immediate actions include disabling the problematic TCP profile options across all affected virtual servers and monitoring for any signs of exploitation attempts. Organizations should also implement network segmentation to limit the impact of potential exploitation and establish monitoring procedures to detect unusual traffic patterns that might trigger the vulnerability. The patching process requires careful planning as it may involve system downtime and requires verification that the updated software maintains all required functionality. Security teams should also consider implementing intrusion detection systems that can identify patterns consistent with exploitation attempts of this vulnerability, as the attack vectors are somewhat predictable but require specific conditions to be effective.