CVE-2018-5500 in BIG-IP
Summary
by MITRE
On F5 BIG-IP systems running 13.0.0, 12.1.0 - 12.1.3.1, or 11.6.1 - 11.6.2, every Multipath TCP (MCTCP) connection established leaks a small amount of memory. Virtual server using TCP profile with Multipath TCP (MCTCP) feature enabled will be affected by this issue.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability described in CVE-2018-5500 represents a memory leak issue affecting F5 BIG-IP systems across multiple versions including 13.0.0, 12.1.0 through 12.1.3.1, and 11.6.1 through 11.6.2. This security flaw specifically targets systems configured with Multipath TCP functionality within their TCP profiles, creating a persistent degradation in system performance and resource availability. The issue manifests through the establishment of Multipath TCP connections where each connection results in a small memory leak, accumulating over time and potentially leading to system instability or denial of service conditions.
The technical implementation of this vulnerability stems from improper memory management within the F5 BIG-IP system's handling of Multipath TCP connections. When the MCTCP feature is enabled on virtual servers using TCP profiles, the system fails to properly release allocated memory resources after connection establishment. This memory leak occurs incrementally with each new connection attempt, meaning that even small amounts of leaked memory compound over time to create significant resource exhaustion. The vulnerability falls under CWE-401: Improper Release of Memory, which specifically addresses issues where allocated memory is not properly deallocated, leading to resource exhaustion. The affected systems demonstrate a failure in resource lifecycle management that directly impacts system availability and performance.
From an operational perspective, this vulnerability creates substantial risk for organizations relying on F5 BIG-IP systems for critical network services. The gradual memory leak can lead to progressive system degradation where available memory decreases incrementally with each Multipath TCP connection established. This degradation may not be immediately apparent but will eventually impact system responsiveness and potentially cause service disruption or complete system failure. The vulnerability is particularly concerning in high-traffic environments where numerous connections are established regularly, as the cumulative effect of small memory leaks can rapidly exhaust available system resources. Attackers could potentially exploit this vulnerability to create a denial of service condition by establishing multiple connections to trigger memory exhaustion.
Organizations should implement immediate mitigation strategies including disabling the Multipath TCP feature on affected systems until proper patches are applied. The recommended approach involves reviewing all virtual server configurations to identify those using TCP profiles with MCTCP enabled and disabling this feature. System administrators should also implement monitoring solutions to track memory usage patterns and establish alerting mechanisms for unusual memory consumption trends. Additionally, organizations should prioritize applying the official F5 security patches and updates as soon as they become available, as these updates will contain the necessary fixes to address the memory management issues. The mitigation strategy should also include regular system performance monitoring to detect early signs of resource exhaustion and implementing connection rate limiting where appropriate to reduce the impact of potential exploitation.
The vulnerability demonstrates characteristics consistent with ATT&CK technique T1499.002: Endpoint Denial of Service, where adversaries can consume system resources to deny service to legitimate users. While this vulnerability may not be directly exploitable by malicious actors in the traditional sense, it represents a significant risk for systems that rely heavily on Multipath TCP functionality. The memory leak creates a condition where system availability is gradually compromised, potentially leading to service interruption that affects business operations. Organizations should also consider this vulnerability in the context of their overall security posture and ensure that their incident response procedures include protocols for handling resource exhaustion issues. The remediation process should involve comprehensive testing of patched systems to ensure that the memory leak has been resolved and that system performance returns to normal operating conditions.