CVE-2018-5515 in BIG-IP
Summary
by MITRE
On F5 BIG-IP 13.0.0-13.1.0.5, using RADIUS authentication responses from a RADIUS server with IPv6 addresses may cause TMM to crash, leading to a failover event.
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Analysis
by VulDB Data Team • 03/08/2023
The vulnerability identified as CVE-2018-5515 affects F5 BIG-IP systems running versions 13.0.0 through 13.1.0.5, specifically when these systems process RADIUS authentication responses containing IPv6 addresses. This issue represents a significant reliability concern within enterprise network infrastructure, as it directly impacts the stability and availability of critical security services. The vulnerability resides in the Traffic Management Microkernel (TMM) component of the BIG-IP platform, which is responsible for processing network traffic and enforcing security policies. When the TMM encounters RADIUS responses with IPv6 addresses, it fails to properly handle the data structure, resulting in a system crash that triggers an automatic failover event. This behavior violates fundamental principles of system resilience and fault tolerance that are essential for maintaining continuous network operations in production environments.
The technical flaw stems from inadequate input validation within the RADIUS authentication processing module of the TMM. When processing authentication responses from RADIUS servers, the system does not properly validate or sanitize IPv6 address formats within the response data. This parsing error occurs during the authentication flow when the system attempts to process the network access server address field in the RADIUS response. The vulnerability can be categorized under CWE-129 as an insufficient input validation issue, where the system fails to properly validate the boundaries and formats of input data. The specific implementation flaw manifests when the TMM encounters IPv6 addresses that exceed expected data structure limits or contain malformed elements, causing memory corruption and subsequent system termination.
The operational impact of this vulnerability extends beyond simple service disruption, creating cascading effects throughout the network infrastructure that rely on F5 BIG-IP systems for load balancing and application delivery. When the TMM crashes and triggers failover, it can result in temporary service interruption as the system transitions to the standby unit, potentially affecting thousands of concurrent connections and user sessions. This vulnerability particularly impacts organizations using RADIUS authentication for network access control, as it can be exploited through legitimate authentication requests containing IPv6 addresses. The automatic failover mechanism, while designed for redundancy, creates additional operational overhead and potential service degradation during the transition period. Organizations may experience increased administrative burden as system administrators must monitor and manage the failover events, while also dealing with potential performance impacts from the redundant system activation.
Mitigation strategies for CVE-2018-5515 should prioritize immediate patching of affected systems to the latest available F5 BIG-IP releases that contain the necessary security fixes. Organizations should also implement network monitoring to detect and alert on unusual authentication traffic patterns that might indicate exploitation attempts. The recommended approach includes configuring RADIUS servers to use IPv4 addresses exclusively when communicating with BIG-IP systems, or implementing network segmentation to isolate RADIUS servers that might send IPv6 addresses. Additionally, system administrators should review and test failover procedures to ensure minimal impact during potential crash events, while also implementing comprehensive logging and alerting mechanisms to quickly identify and respond to authentication-related system failures. This vulnerability aligns with ATT&CK technique T1566 which covers credential access through network authentication systems, highlighting the importance of maintaining secure authentication infrastructure in enterprise environments.