CVE-2018-15443 in Firepower System Software
Summary
by MITRE
A vulnerability in the detection engine of Cisco Firepower System Software could allow an unauthenticated, remote attacker to bypass a configured Intrusion Prevention System (IPS) rule that inspects certain types of TCP traffic. The vulnerability is due to incorrect TCP retransmission handling. An attacker could exploit this vulnerability by sending a crafted TCP connection request through an affected device. A successful exploit could allow the attacker to bypass configured IPS rules and allow uninspected traffic onto the network.
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Analysis
by VulDB Data Team • 06/05/2023
The vulnerability identified as CVE-2018-15443 resides within the detection engine of Cisco Firepower System Software, representing a critical security flaw that undermines the integrity of Intrusion Prevention System operations. This weakness specifically targets the handling of TCP retransmissions within the network security infrastructure, creating a pathway for malicious actors to circumvent protective measures that are meant to inspect and control TCP traffic flows. The flaw operates at a fundamental level of network protocol processing, where the system fails to properly account for legitimate TCP retransmission scenarios during its inspection processes.
The technical root cause of this vulnerability stems from the incorrect processing of TCP retransmission packets within the Firepower detection engine. When TCP connections experience retransmissions due to packet loss or network delays, the system's inspection mechanism fails to properly recognize these legitimate retransmission patterns, causing it to either ignore or misinterpret the traffic flow. This misidentification results in the system treating retransmitted packets as new connections or as traffic that does not require inspection, effectively creating blind spots in the IPS protection framework. The vulnerability manifests when an attacker crafts TCP connection requests that exploit this retransmission handling flaw to bypass security rules that would normally inspect and potentially block suspicious TCP traffic.
Operationally, this vulnerability presents a significant risk to network security posture as it allows unauthenticated remote attackers to bypass configured IPS rules without requiring any credentials or privileged access. The attack vector is particularly concerning because it leverages normal TCP behavior to achieve malicious objectives, making the exploit difficult to detect through conventional monitoring methods. Successful exploitation enables attackers to inject uninspected traffic into the network, potentially allowing malware delivery, command and control communications, or other malicious activities to proceed undetected. The impact extends beyond simple bypass of security controls to potentially enable more sophisticated attacks that rely on evading network monitoring systems, as the retransmitted traffic may contain payloads that would normally be flagged by the IPS.
Organizations utilizing Cisco Firepower systems must implement immediate mitigations to address this vulnerability, including applying the latest security patches released by Cisco to correct the TCP retransmission handling logic. Network administrators should also consider implementing additional monitoring controls to detect anomalous TCP retransmission patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-119, which addresses improper restriction of operations within a recognized security boundary, and represents a significant concern under ATT&CK framework category T1071.004 for application layer protocol traffic shaping. Organizations should conduct comprehensive vulnerability assessments to identify any potential exploitation attempts and establish network segmentation controls to limit the impact of successful bypasses, while also reviewing their overall network security architecture to ensure adequate protection against similar protocol-level vulnerabilities that could compromise other security controls.