CVE-2019-6594 in BIG-IP
Summary
by MITRE
On BIG-IP 11.5.1-11.6.3.2, 12.1.3.4-12.1.3.7, 13.0.0 HF1-13.1.1.1, and 14.0.0-14.0.0.2, Multi-Path TCP (MPTCP) does not protect against multiple zero length DATA_FINs in the reassembly queue, which can lead to an infinite loop in some circumstances.
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Analysis
by VulDB Data Team • 07/19/2023
The vulnerability described in CVE-2019-6594 affects F5 BIG-IP systems running specific versions of the BIG-IP operating system including 11.5.1 through 11.6.3.2, 12.1.3.4 through 12.1.3.7, 13.0.0 HF1 through 13.1.1.1, and 14.0.0 through 14.0.0.2. This issue resides within the Multi-Path TCP implementation which is a network protocol extension designed to improve performance by allowing data to be transmitted over multiple paths simultaneously. The vulnerability specifically targets the reassembly queue mechanism that handles TCP segments during connection termination phases, creating a critical condition that can lead to system instability.
The technical flaw manifests when the MPTCP implementation fails to properly handle multiple zero-length DATA_FIN segments that may accumulate in the reassembly queue during connection teardown. These zero-length segments typically indicate the end of data transmission on a particular path within the multipath connection. However, the system's failure to adequately process these segments results in an infinite loop condition where the system continuously processes the same segments without proper termination, consuming excessive CPU resources and potentially causing system hangs or crashes. This behavior represents a classic denial of service vulnerability that can be exploited by remote attackers.
The operational impact of this vulnerability is significant for organizations relying on F5 BIG-IP systems for their network infrastructure. The infinite loop condition can lead to complete service disruption as the system becomes unresponsive to legitimate traffic while consuming all available processing resources. Network administrators may experience prolonged outages, increased system load, and potential data loss during the period when the system is caught in the loop. The vulnerability affects the core functionality of the load balancing and traffic management capabilities that BIG-IP systems provide, making it particularly dangerous in production environments where availability is critical.
This vulnerability maps to CWE-835, which specifically addresses the issue of infinite loops in software implementations, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. Organizations should implement immediate mitigations including applying the latest security patches provided by F5, configuring rate limiting on MPTCP connections, and monitoring for unusual CPU utilization patterns that may indicate the vulnerability is being exploited. Network segmentation and intrusion detection systems should also be configured to detect anomalous MPTCP traffic patterns that could indicate exploitation attempts. The recommended remediation approach involves upgrading to patched versions of the BIG-IP software and implementing proper monitoring procedures to detect potential exploitation attempts before they can cause significant disruption to network services.