CVE-2019-6619 in BIG-IP
Summary
by MITRE
On BIG-IP 14.0.0-14.1.0.1, 13.0.0-13.1.1.4, and 12.1.0-12.1.4, the Traffic Management Microkernel (TMM) may restart when a virtual server has an HTTP/2 profile with Application Layer Protocol Negotiation (ALPN) enabled and it processes traffic where the ALPN extension size is zero.
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Analysis
by VulDB Data Team • 09/12/2023
The vulnerability described in CVE-2019-6619 represents a critical denial of service weakness affecting F5 BIG-IP appliances across multiple versions including 12.1.0 through 12.1.4, 13.0.0 through 13.1.1.4, and 14.0.0 through 14.1.0.1. This issue specifically targets the Traffic Management Microkernel component which serves as the core processing engine for handling network traffic in F5's load balancing and application delivery solutions. The flaw manifests when the system processes HTTP/2 traffic with Application Layer Protocol Negotiation enabled on virtual servers, creating a condition where the TMM component becomes unstable and restarts unexpectedly. This behavior directly violates the fundamental availability principles of network infrastructure services and represents a significant operational risk for organizations relying on F5 BIG-IP appliances for critical application delivery.
The technical root cause of this vulnerability lies in the improper handling of HTTP/2 protocol extensions within the TMM processing pipeline. When an HTTP/2 virtual server is configured with ALPN enabled and receives traffic containing an ALPN extension with zero size, the TMM fails to properly validate or handle this edge case, leading to a memory corruption or state management error that ultimately triggers the component restart. This represents a classic buffer over-read or improper input validation scenario where the system does not adequately check the size parameter of protocol extensions before processing them. The vulnerability falls under the CWE-121 category of buffer overflow conditions and aligns with ATT&CK technique T1499.004 for network denial of service attacks. The specific nature of the flaw suggests that the TMM's HTTP/2 processing code lacks proper bounds checking for ALPN extension sizes, particularly when the extension length is zero, which should be a valid edge case in protocol implementations.
The operational impact of CVE-2019-6619 extends beyond simple service disruption to potentially compromise the availability of critical business applications and services. When the TMM restarts due to this vulnerability, it causes immediate disruption to all HTTP/2 traffic flowing through affected virtual servers, leading to connection drops, application timeouts, and potential data loss for users. Organizations utilizing F5 BIG-IP appliances for mission-critical applications face significant risk of service degradation or complete outages during exploitation of this vulnerability. The restart behavior creates a cascading effect that can overwhelm system monitoring and alerting mechanisms, making it difficult for security teams to distinguish between legitimate system maintenance and actual attack conditions. This vulnerability particularly affects environments with high-volume HTTP/2 traffic, such as modern web applications, microservices architectures, and content delivery networks where ALPN is commonly enabled for protocol optimization.
Mitigation strategies for CVE-2019-6619 should prioritize immediate implementation of F5's official security patches and updates, as these address the root cause through proper input validation and bounds checking mechanisms. Organizations should disable ALPN profiles on virtual servers when not required, particularly in environments where the vulnerability is actively exploited. Network segmentation and monitoring controls should be enhanced to detect unusual TMM restart patterns that may indicate exploitation attempts. Implementing rate limiting and traffic filtering mechanisms at the network perimeter can help reduce the impact of potential attacks. Security teams should also establish automated monitoring for TMM restart events and implement proper incident response procedures to quickly address any exploitation attempts. Regular vulnerability assessments and penetration testing should be conducted to identify other potential protocol handling issues within the BIG-IP appliance configuration. The remediation process should include comprehensive testing of patched systems to ensure that the fix does not introduce compatibility issues with existing HTTP/2 applications and services.