CVE-2019-6683 in BIG-IP Virtual Server
Summary
by MITRE
On versions 15.0.0-15.0.1.1, 14.1.0-14.1.2.2, 14.0.0-14.0.1, 13.1.0-13.1.3.2, 12.1.0-12.1.5, and 11.5.2-11.6.5.1, BIG-IP virtual servers with Loose Initiation enabled on a FastL4 profile may be subject to excessive flow usage under undisclosed conditions.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 03/16/2024
The vulnerability identified as CVE-2019-6683 affects F5 BIG-IP systems running specific versions of the BIG-IP operating system including 15.0.0-15.0.1.1, 14.1.0-14.1.2.2, 14.0.0-14.0.1, 13.1.0-13.1.3.2, 12.1.0-12.1.5, and 11.5.2-11.6.5.1. This security flaw resides within the handling of virtual servers that utilize the FastL4 profile with Loose Initiation enabled, representing a critical concern for network infrastructure administrators who rely on F5's load balancing and application delivery capabilities. The vulnerability stems from the improper management of network flow states when processing incoming connections, creating a condition where the system's flow table can become excessively consumed under certain circumstances.
The technical flaw manifests when the FastL4 profile operates with Loose Initiation enabled on virtual servers, allowing for connections to be established without proper validation of the initial connection handshake. This configuration creates a scenario where the system maintains flow entries for connections that may never complete or are otherwise malformed, leading to a gradual depletion of available flow table resources. The vulnerability is particularly concerning because the exact conditions triggering this excessive flow consumption remain undisclosed, making it difficult for administrators to predict or prevent the issue. This behavior aligns with CWE-129, which addresses improper validation of input boundaries, and represents a form of resource exhaustion attack that can effectively disrupt service availability.
The operational impact of CVE-2019-6683 extends beyond simple performance degradation to potentially causing complete service disruption across affected BIG-IP systems. When flow tables become exhausted, the system cannot properly handle new incoming connections, resulting in connection failures and application downtime that directly impacts business operations. Network administrators may observe symptoms including increased connection timeouts, reduced throughput, and overall system instability in environments where the vulnerable configurations are deployed. The vulnerability's nature makes it particularly dangerous in high-traffic environments where the flow table is already operating near capacity, as the excessive consumption can occur rapidly and without warning. Organizations implementing F5 BIG-IP solutions in production environments must consider the potential for cascading failures when this vulnerability is present, as the system's inability to process new connections can affect downstream services and applications.
Mitigation strategies for CVE-2019-6683 require immediate attention from system administrators and security teams responsible for F5 BIG-IP deployments. The primary recommendation involves upgrading affected BIG-IP systems to versions that contain patches addressing this vulnerability, as F5 has released updates specifically targeting this issue. Administrators should also consider disabling Loose Initiation on FastL4 profiles when it is not strictly required for application functionality, as this configuration change can prevent the vulnerable code path from being triggered. Additionally, implementing monitoring solutions that track flow table utilization and connection states can help detect early signs of the vulnerability manifesting in production environments. Organizations should also review their current BIG-IP configurations to identify all virtual servers using FastL4 profiles with Loose Initiation enabled, and systematically remediate these configurations according to F5's official security advisories. The ATT&CK framework categorizes this vulnerability under resource exhaustion techniques, specifically targeting system resources through improper flow management, making it a critical concern for organizations implementing network security controls that rely on consistent flow handling.