CVE-2019-6638 in BIG-IP
Summary
by MITRE
On BIG-IP 14.1.0-14.1.0.5 and 14.0.0-14.0.0.4, Malformed http requests made to an undisclosed iControl REST endpoint can lead to infinite loop of the restjavad process.
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Analysis
by VulDB Data Team • 10/17/2023
The vulnerability described in CVE-2019-6638 represents a critical denial of service weakness within F5 BIG-IP systems that affects versions 14.1.0 through 14.1.0.5 and 14.0.0 through 14.0.0.4. This flaw manifests when malformed http requests are sent to an undisclosed iControl REST endpoint, creating a condition where the restjavad process enters an infinite loop. The iControl REST API serves as the primary interface for managing BIG-IP systems remotely, making this vulnerability particularly concerning for network security operations. The infinite loop behavior causes the restjavad process to consume excessive cpu resources continuously, effectively rendering the management interface unavailable and compromising the system's operational integrity.
This vulnerability directly maps to CWE-835, which specifically addresses the issue of infinite loops in software systems, and falls under the broader category of denial of service conditions that can be triggered through input manipulation. The technical flaw exploits the lack of proper input validation within the iControl REST endpoint implementation, allowing attackers to craft malicious http requests that bypass normal processing logic. When the restjavad process encounters these malformed requests, it fails to properly terminate execution or handle the abnormal input, instead falling into a continuous processing cycle that consumes system resources without resolution. The undisclosed nature of the specific endpoint adds to the complexity of both exploitation and mitigation efforts, as administrators cannot easily identify or restrict access to the vulnerable interface.
The operational impact of this vulnerability extends beyond simple service disruption, as it can severely compromise network availability and management capabilities for organizations relying on BIG-IP systems for load balancing, application delivery, and security services. When the restjavad process becomes unresponsive due to the infinite loop, administrators lose access to critical management functions including configuration changes, monitoring capabilities, and system status reporting. This situation creates a cascading effect where network operations become impaired, potentially leading to service degradation or complete outages for applications dependent on the affected BIG-IP appliances. The vulnerability also impacts the system's ability to respond to legitimate management requests, as the process remains occupied with processing the malicious requests.
Organizations should implement immediate mitigations including applying the vendor-provided security patches and updates released for this vulnerability, which typically include enhanced input validation and proper exception handling for the iControl REST endpoints. Network segmentation and access controls should be enforced to limit exposure of the affected systems to trusted management networks only, while monitoring solutions should be deployed to detect unusual cpu utilization patterns that may indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1499.004 for endpoint denial of service, emphasizing the importance of maintaining system availability and implementing robust process monitoring. Additionally, administrators should consider implementing rate limiting and request validation mechanisms at network boundaries to prevent malformed requests from reaching the vulnerable endpoints, while maintaining comprehensive logging of management interface access for forensic analysis purposes.