CVE-2018-5512 in BIG-IP
Summary
by MITRE
On F5 BIG-IP 13.1.0-13.1.0.5, when Large Receive Offload (LRO) and SYN cookies are enabled (default settings), undisclosed traffic patterns may cause TMM to restart.
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Analysis
by VulDB Data Team • 03/08/2023
The vulnerability identified as CVE-2018-5512 affects F5 BIG-IP systems running version 13.1.0 through 13.1.0.5 where specific network configuration settings create a condition that can lead to system instability. This issue manifests when both Large Receive Offload and SYN cookies features are enabled simultaneously, which represents the default configuration for these systems. The flaw operates at the network processing level where the Traffic Management Microkernel (TMM) component encounters specific traffic patterns that trigger an unexpected restart sequence. The vulnerability demonstrates a critical weakness in how the system handles network packet processing under certain load conditions, particularly when these two optimization features interact in ways that were not fully anticipated during the system design phase.
The technical mechanism behind this vulnerability involves the interaction between LRO and SYN cookies functionality within the TMM processing pipeline. LRO is designed to improve network performance by allowing the reception of large packets that would normally be fragmented, while SYN cookies serve as a defense mechanism against SYN flood attacks by encoding connection information in the SYN-ACK response. When these features operate concurrently with specific traffic patterns, the packet processing logic within TMM encounters a condition that causes the system to crash and restart automatically. This behavior represents a denial of service vulnerability that can be exploited to disrupt network services without requiring authentication or specialized access privileges. The vulnerability falls under CWE-682 Incorrect Calculation, as it involves a miscalculation in how packet processing interacts with system resources under specific conditions.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network availability and reliability for organizations relying on F5 BIG-IP systems for their critical infrastructure. When the TMM restarts, all active connections are terminated and must be re-established, leading to service interruptions that can affect business operations and user experience. The vulnerability is particularly concerning because it operates silently in the background, with no specific error messages or alerts indicating the underlying issue, making it difficult to detect and diagnose. Network administrators may observe intermittent service disruptions or connection failures without immediately identifying the root cause as this specific interaction between LRO and SYN cookies settings. The default configuration of these features means that organizations are vulnerable by default, requiring them to actively modify system settings to mitigate the risk.
Mitigation strategies for CVE-2018-5512 should focus on either disabling one of the conflicting features or applying the vendor-provided security patches. Organizations can address this vulnerability by disabling either Large Receive Offload or SYN cookies functionality, though this may impact network performance and security respectively. The preferred approach involves applying the official F5 security patches that address the specific interaction between these features. System administrators should also implement monitoring solutions to detect unusual restart patterns that might indicate this vulnerability is being triggered. Network segmentation and redundancy planning can help minimize the impact of potential service disruptions. From an ATT&CK framework perspective, this vulnerability aligns with T1499.004, which covers evasion techniques involving system restarts and service disruption, though the vulnerability itself represents an unintended consequence rather than an intentional attack vector. The incident response procedures should include verification of system configurations and implementation of proper change management processes to prevent unintended activation of vulnerable settings.