CVE-2025-59147 is a high-severity vulnerability affecting Suricata, an open-source network intrusion detection system (IDS), intrusion prevention system (IPS), and network security monitoring (NSM) engine developed by the Open Information Security Foundation (OISF). The vulnerability arises from an improperly implemented security check related to TCP session handling, specifically when Suricata processes multiple SYN packets with differing sequence numbers within the same flow tuple. In affected versions (all versions prior to 7.0.12 and versions 8.0.0 up to but not including 8.0.1), this crafted traffic can cause Suricata to fail to correctly track the TCP session. In IDS mode, this failure leads to detection and logging bypass, meaning malicious traffic can pass through without being detected or recorded. In IPS mode, the flaw causes the flow to be blocked, which may result in unintended denial of service for legitimate traffic. The root cause is categorized under CWE-358, indicating an improperly implemented security check. The vulnerability has a CVSS v3.1 base score of 7.5, reflecting a high severity due to its network attack vector, low complexity, no required privileges or user interaction, and significant impact on integrity (ability to bypass detection). No known exploits are currently reported in the wild. The issue is resolved in Suricata versions 7.0.12 and 8.0.1, where the TCP session handling logic has been corrected to properly handle multiple SYN packets with different sequence numbers within the same flow tuple, ensuring accurate session tracking and detection.

For European organizations, the impact of CVE-2025-59147 can be significant, especially for those relying on Suricata for network security monitoring and intrusion detection/prevention. In IDS deployments, attackers can craft network traffic to bypass detection, allowing malicious activities such as data exfiltration, lateral movement, or command and control communications to go unnoticed. This undermines the integrity of security monitoring and increases the risk of prolonged undetected breaches. In IPS deployments, the vulnerability may cause legitimate traffic flows to be blocked erroneously, potentially disrupting business-critical communications and causing availability issues. Organizations in sectors with high security requirements—such as finance, critical infrastructure, telecommunications, and government—may face increased risk of targeted attacks leveraging this bypass. Additionally, the inability to detect or properly log malicious traffic complicates incident response and forensic investigations. Given the network-based nature of the vulnerability and the widespread use of Suricata in European enterprises and public sector networks, the threat could affect a broad range of organizations if patches are not applied promptly.

To mitigate CVE-2025-59147, European organizations should prioritize upgrading Suricata to versions 7.0.12 or 8.0.1 or later, where the vulnerability is fixed. Network security teams must verify their Suricata deployment versions and plan immediate patching to eliminate the detection bypass risk. In parallel, organizations should review and enhance their network traffic monitoring to detect anomalous patterns indicative of SYN packet manipulation or session hijacking attempts. Deploying complementary network security tools that do not rely solely on Suricata for TCP session tracking can provide defense in depth. Additionally, organizations should implement strict network segmentation and enforce least privilege principles to limit the potential impact of undetected malicious traffic. Regular security audits and penetration testing should include attempts to exploit this vulnerability to validate the effectiveness of applied patches. Finally, maintaining up-to-date threat intelligence feeds and monitoring vendor advisories will help organizations respond quickly to any emerging exploit attempts.