CVE-2019-6677 in BIG-IP
Summary
by MITRE
On BIG-IP versions 15.0.0-15.0.1, 14.1.0-14.1.2, 14.0.0-14.0.1, 13.1.0-13.1.3.1, and 12.1.0-12.1.5, under certain conditions when using custom TCP congestion control settings in a TCP profile, TMM stops processing traffic when processed by an iRule.
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Analysis
by VulDB Data Team • 03/16/2024
The vulnerability identified as CVE-2019-6677 affects F5 BIG-IP application delivery controllers across multiple version ranges including 15.0.0-15.0.1, 14.1.0-14.1.2, 14.0.0-14.0.1, 13.1.0-13.1.3.1, and 12.1.0-12.1.5. This issue represents a critical denial of service condition that impacts the Traffic Management Microkernel (TMM) component responsible for processing network traffic. The vulnerability manifests specifically when custom TCP congestion control settings are configured within TCP profiles and subsequently processed by iRules, creating a scenario where the system becomes unresponsive to incoming network traffic. This flaw operates at the core of the BIG-IP platform's traffic processing capabilities and directly affects the availability of services delivered through the appliance.
The technical mechanism behind this vulnerability involves a specific interaction between TCP profile configurations and iRule execution within the TMM processing pipeline. When custom TCP congestion control parameters are applied to TCP profiles and these profiles are subsequently invoked by iRules, a condition occurs that causes the TMM to cease processing network packets entirely. This behavior constitutes a software defect that falls under CWE-691, which specifically addresses insufficient control flow management and inadequate handling of control flow in software systems. The issue demonstrates poor resource management and control flow handling within the BIG-IP traffic processing architecture, where the system fails to maintain proper operational states during complex traffic processing scenarios involving custom TCP parameters and iRule execution contexts.
The operational impact of CVE-2019-6677 extends beyond simple service disruption to represent a severe availability threat that can compromise entire network infrastructures relying on F5 BIG-IP appliances. Organizations utilizing these vulnerable versions may experience complete service outages where network traffic ceases to be processed, affecting critical applications and services. The vulnerability affects both the application delivery and network infrastructure layers, potentially impacting business continuity and customer experience. Security teams must consider this vulnerability in their risk assessment frameworks as it can be exploited to create denial of service conditions that are difficult to detect and remediate. The impact is particularly concerning given that the vulnerability affects multiple major version lines, indicating a fundamental flaw in the platform's traffic processing logic rather than a localized issue.
Mitigation strategies for CVE-2019-6677 require immediate attention from network security administrators and system operators. The primary recommended approach involves applying the official F5 security patches released to address this vulnerability, which typically include updated TMM components and corrected TCP profile handling logic. Organizations should also consider temporarily disabling custom TCP congestion control settings and iRule configurations that trigger the problematic code path until patches can be properly deployed and tested. Network segmentation strategies may be employed to limit the blast radius of potential exploitation, while monitoring systems should be enhanced to detect unusual traffic processing patterns that might indicate the vulnerability being exploited. The remediation process must include comprehensive testing in non-production environments to ensure that patch deployment does not introduce regressions in existing functionality, particularly in complex network environments where multiple iRules and TCP profiles interact. Additionally, organizations should review their iRule implementations to identify and eliminate potentially problematic configurations that could trigger this vulnerability, following ATT&CK framework principles for network service disruption and application layer attacks.