CVE-2019-6645 in BIG-IP
Summary
by MITRE
On BIG-IP 14.0.0-14.1.0.5, 13.0.0-13.1.2, 12.1.0-12.1.4.1, 11.5.2-11.6.4, FTP traffic passing through a Virtual Server with both an active FTP profile associated and connection mirroring configured may lead to a TMM crash causing the configured HA action to be taken.
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Analysis
by VulDB Data Team • 12/13/2023
The vulnerability described in CVE-2019-6645 represents a critical denial of service weakness affecting F5 BIG-IP systems across multiple software versions. This issue specifically targets the Traffic Management Microkernel (TMM) component within the BIG-IP platform, which is responsible for processing network traffic and enforcing security policies. The flaw manifests when FTP traffic traverses a Virtual Server that has both an active FTP profile and connection mirroring enabled, creating a scenario where the system's processing logic fails catastrophically. The vulnerability falls under CWE-119 which addresses improper access to memory locations, specifically indicating a potential buffer overflow or memory corruption issue that occurs during the processing of FTP traffic flows. This weakness is particularly concerning because it can trigger a complete system crash, effectively rendering the affected BIG-IP appliance non-functional and disrupting critical network services.
The technical mechanism behind this vulnerability involves the interaction between FTP protocol handling and connection mirroring functionality within the BIG-IP architecture. When an FTP session is established through a Virtual Server configured with both an active FTP profile and connection mirroring, the system attempts to maintain synchronized connection states between primary and secondary devices in an HA configuration. The flaw occurs during the processing of FTP control and data channel communications, where malformed or specific traffic patterns cause the TMM process to encounter a critical error that results in an immediate system crash. This crash is not merely a service interruption but a complete kernel-level failure that forces the system to reboot or enter an unrecoverable state. The vulnerability is particularly dangerous because it can be triggered remotely through normal FTP traffic without requiring authentication or specialized privileges, making it an attractive target for malicious actors seeking to disrupt network services.
The operational impact of CVE-2019-6645 extends far beyond simple service disruption, as it can severely compromise the availability and reliability of critical network infrastructure. Organizations relying on BIG-IP appliances for load balancing, application delivery, and security enforcement face significant risks when this vulnerability is exploited, particularly in environments where high availability is paramount. The configured HA actions that are triggered upon system crash can lead to unintended failover scenarios, potentially causing cascading failures across network infrastructure and disrupting business operations. From an attacker perspective, this vulnerability provides a straightforward method for conducting denial of service attacks against critical network services, making it particularly dangerous in environments where network availability is essential. The vulnerability affects multiple versions of the BIG-IP software, indicating a widespread exposure across organizations that may have various system configurations and update schedules. The lack of authentication requirements for exploitation means that even unauthenticated attackers can potentially trigger the crash, making it a significant threat to network availability.
Organizations should implement immediate mitigations including applying the official F5 security patches released in response to this vulnerability, which address the underlying memory handling issues in the TMM component. Network segmentation and access control measures should be strengthened to limit exposure of vulnerable BIG-IP appliances to untrusted networks, particularly by restricting FTP traffic access to authorized systems only. Monitoring should be enhanced to detect unusual traffic patterns that might indicate exploitation attempts, with specific attention to FTP protocol handling and connection mirroring configurations. The vulnerability demonstrates the importance of proper input validation and memory management in network security appliances, aligning with ATT&CK technique T1499 which covers network disruption attacks. System administrators should also consider temporarily disabling connection mirroring on affected Virtual Servers while patches are deployed, and implementing comprehensive logging to track FTP traffic patterns that might trigger the vulnerability. Regular vulnerability assessments and security audits should be conducted to identify similar weaknesses in other network infrastructure components, as this vulnerability highlights the critical need for robust memory safety practices in security appliance design and implementation.