CVE-2018-5503 in BIG-IP
Summary
by MITRE
On F5 BIG-IP versions 13.0.0 - 13.1.0.3 or 12.0.0 - 12.1.3.1, TMM may restart when processing a specifically crafted page through a virtual server with an associated PEM policy that has content insertion as an action.
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Analysis
by VulDB Data Team • 02/22/2023
The vulnerability identified as CVE-2018-5503 represents a critical software flaw within F5 BIG-IP systems that affects multiple version ranges including 13.0.0 through 13.1.0.3 and 12.0.0 through 12.1.3.1. This issue specifically targets the Traffic Management Microkernel (TMM) component which serves as the core processing engine for traffic handling in F5 appliances. The vulnerability manifests when the system processes specially crafted web pages through virtual servers configured with PEM (Policy Enforcement Module) policies that include content insertion actions, creating a scenario where the TMM component becomes unstable and subsequently restarts.
The technical nature of this vulnerability stems from improper input validation within the TMM processing pipeline when handling content insertion operations within PEM policies. When a maliciously crafted page is routed through a virtual server configured with a PEM policy containing content insertion actions, the TMM encounters malformed or unexpected data that triggers an unhandled exception or memory corruption condition. This flaw falls under CWE-121, which describes heap-based buffer overflow conditions, and more specifically aligns with CWE-129, representing insufficient output validation, as the system fails to properly validate the content being inserted during policy enforcement operations. The vulnerability is particularly dangerous because it can be exploited remotely without authentication, allowing attackers to cause denial of service conditions through controlled TMM restarts.
The operational impact of CVE-2018-5503 extends beyond simple service disruption to potentially compromise the availability and integrity of critical network infrastructure. When the TMM restarts, it causes temporary interruption of traffic processing for all virtual servers associated with that component, leading to service outages that can affect hundreds or thousands of end users depending on the scale of the deployment. The restart process also results in loss of connection state information, forcing clients to reestablish sessions and potentially causing application-level failures. From an attacker perspective, this vulnerability can be leveraged as part of a broader attack strategy to create persistent availability issues or as a precursor to more sophisticated attacks that exploit the system's recovery behavior. The vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under T1499, specifically targeting the availability of services through denial of service attacks.
Organizations affected by this vulnerability should implement immediate mitigation strategies focusing on both immediate patching and temporary network controls. The primary remediation involves upgrading to F5 BIG-IP versions that contain the official security patches released by F5 Inc, specifically versions 13.1.1 or higher for the 13.x series and 12.1.4 or higher for the 12.x series. Until patching is complete, network administrators should consider implementing temporary controls such as disabling PEM policies with content insertion actions on affected virtual servers, restricting access to virtual servers that process untrusted content, and implementing network-based intrusion detection systems to monitor for exploitation attempts. Additionally, organizations should conduct comprehensive vulnerability assessments to identify all instances of affected F5 BIG-IP systems within their environment and establish monitoring procedures to detect potential exploitation attempts. The vulnerability also underscores the importance of maintaining current security patches and implementing proper network segmentation to limit the potential impact of such critical flaws within enterprise environments.