CVE-2019-6623 in BIG-IP
Summary
by MITRE
On BIG-IP 14.1.0-14.1.0.5, 14.0.0-14.0.0.4, 13.0.0-13.1.1.4, and 12.1.0-12.1.4, undisclosed traffic sent to BIG-IP iSession virtual server may cause the Traffic Management Microkernel (TMM) to restart, resulting in a Denial-of-Service (DoS).
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Analysis
by VulDB Data Team • 10/15/2023
The vulnerability identified as CVE-2019-6623 represents a critical denial-of-service weakness within F5 Networks BIG-IP systems that affects multiple versions of the Traffic Management Microkernel. This flaw specifically targets the iSession virtual server functionality where improperly formatted or malicious traffic can trigger unexpected behavior in the TMM process. The vulnerability exists in versions 14.1.0 through 14.1.0.5, 14.0.0 through 14.0.0.4, 13.0.0 through 13.1.1.4, and 12.1.0 through 12.1.4 of the BIG-IP platform, making it a widespread issue affecting a significant portion of F5's deployment base. The root cause lies in insufficient input validation within the iSession handling mechanism, where the system fails to properly process malformed traffic packets directed toward the virtual server configuration.
The technical exploitation of this vulnerability occurs when specifically crafted traffic is transmitted to the iSession virtual server endpoint, causing the Traffic Management Microkernel to encounter an unexpected condition that results in its immediate restart. This process restarts the TMM service, which serves as the core component responsible for traffic processing and load balancing operations within the BIG-IP system. The restart process effectively terminates all active connections and prevents the system from processing new traffic, thereby creating a complete denial-of-service condition for legitimate users. This behavior aligns with CWE-20, which describes improper input validation as a fundamental weakness that can lead to system instability and service disruption.
From an operational impact perspective, this vulnerability presents a severe threat to network availability and business continuity for organizations relying on F5 BIG-IP systems for their traffic management needs. The DoS condition can be triggered remotely with minimal technical expertise, making it particularly dangerous in production environments where continuous availability is critical. Network administrators may experience unexpected service interruptions that could affect customer access to applications, particularly in scenarios where the BIG-IP system serves as a critical gateway for enterprise or internet-facing services. The vulnerability's impact extends beyond simple service interruption as it can potentially affect high-availability configurations and failover mechanisms that depend on consistent TMM operation.
Organizations affected by CVE-2019-6623 should implement immediate mitigations including applying the official F5 security patches released for the affected versions, which address the input validation issues within the iSession handling code. Network segmentation and access control measures can provide temporary protection by limiting exposure of the vulnerable iSession virtual server endpoints to untrusted networks. Monitoring and alerting systems should be enhanced to detect unusual traffic patterns or service restarts that may indicate exploitation attempts. Additionally, implementing rate limiting and traffic filtering rules at network boundaries can help reduce the attack surface and provide defense-in-depth measures. This vulnerability demonstrates the importance of maintaining current security patches and following security advisories from vendors, as outlined in the MITRE ATT&CK framework's methodology for identifying and mitigating system-level vulnerabilities. Organizations should also consider implementing network intrusion detection systems that can identify patterns associated with this specific DoS attack vector, as the restart behavior creates distinctive network traffic signatures that can be monitored and blocked.