CVE-2019-6686 in BIG-IP
Summary
by MITRE
On BIG-IP versions 15.0.0-15.0.1.1, 14.1.0-14.1.2, 14.0.0-14.0.1, 13.1.0-13.1.3.1, the Traffic Management Microkernel (TMM) might stop responding after the total number of diameter connections and pending messages on a single virtual server has reached 32K.
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Analysis
by VulDB Data Team • 03/16/2024
The vulnerability identified as CVE-2019-6686 affects F5 BIG-IP systems running specific version ranges including 15.0.0 through 15.0.1.1, 14.1.0 through 14.1.2, 14.0.0 through 14.0.1, and 13.1.0 through 13.1.3.1. This issue resides within the Traffic Management Microkernel component which serves as the core processing engine for traffic handling on F5 devices. The flaw manifests when the system reaches a specific threshold of diameter connections and pending messages on individual virtual servers, creating a condition that leads to complete system unresponsiveness. The diameter protocol is commonly used in telecommunications for authentication, authorization, and accounting services, making this vulnerability particularly concerning for network infrastructure providers and service operators who rely on F5 BIG-IP appliances for their traffic management needs. This vulnerability represents a critical denial of service condition that can result in complete service interruption for affected systems.
The technical root cause of CVE-2019-6686 stems from inadequate memory management and resource tracking within the TMM component of the BIG-IP system. When the cumulative count of diameter connections and pending messages on a single virtual server reaches exactly 32,000 items, the system enters a state where the TMM process becomes unresponsive and ceases to process further traffic. This threshold represents a hard-coded limit that, when exceeded, triggers a memory allocation or resource management failure within the microkernel. The issue demonstrates poor error handling and resource exhaustion management, where the system fails to gracefully handle high-load conditions rather than implementing proper overflow protection mechanisms. From a cybersecurity perspective, this vulnerability aligns with CWE-400, which covers unspecified resource exhaustion, and CWE-704, addressing improper handling of resource exhaustion conditions. The flaw essentially creates a resource starvation scenario where legitimate traffic cannot be processed due to the system's inability to manage the defined threshold properly.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential business continuity risks for organizations relying on F5 BIG-IP appliances. When the TMM becomes unresponsive, all traffic flowing through the affected virtual servers ceases to be processed, potentially affecting critical network services including web applications, database connections, and telecommunications services that depend on diameter protocol communication. The timing of this failure is particularly problematic as it occurs at a predictable threshold, making it potentially exploitable by attackers who could deliberately drive traffic to reach this limit. Organizations may experience extended downtime while system administrators work to identify and resolve the issue, as the complete unresponsiveness of the TMM makes it difficult to perform remote troubleshooting. This vulnerability also affects the availability aspect of the CIA triad, as the system's inability to process legitimate requests constitutes a denial of service condition that can severely impact operational effectiveness and customer service delivery.
Mitigation strategies for CVE-2019-6686 should prioritize immediate patch deployment from F5 as the primary solution, as the vendor has released security updates specifically addressing this resource management issue. Organizations should implement monitoring solutions to track diameter connection counts and pending message queues on virtual servers to identify when thresholds approach the critical 32K limit. Network administrators should consider implementing traffic shaping or rate limiting policies to prevent any single virtual server from accumulating excessive diameter connections and pending messages. The implementation of redundant systems and failover mechanisms becomes crucial for maintaining service availability during patch deployment or when immediate remediation is not possible. From an ATT&CK framework perspective, this vulnerability relates to T1499.004, which covers network disruption, and T1499.001, covering network denial of service attacks. Organizations should also consider implementing intrusion detection systems that can monitor for unusual traffic patterns that might indicate attempts to exploit this vulnerability, as well as establishing incident response procedures specifically tailored to handle TMM unresponsiveness conditions. Regular vulnerability assessments and system health monitoring should include checks for diameter protocol connection thresholds to prevent this condition from occurring in production environments.