Introduction
Attackers can slip malicious traffic past network monitoring, or trigger unnecessary flow blocks, simply by manipulating TCP handshake packets. This is the real-world impact of CVE-2025-59147, a vulnerability in Suricata's TCP session handling that affects a wide range of deployments in both detection and prevention modes.
Suricata is an open-source network intrusion detection and prevention engine developed by the Open Information Security Foundation (OISF). It is widely used in enterprise, service provider, and research networks for deep packet inspection, threat detection, and network security monitoring. Suricata's multi-threaded architecture and protocol parsing capabilities make it a popular choice for high-performance environments.
Technical Information
CVE-2025-59147 is rooted in Suricata's TCP stream tracking and session management subsystem. The vulnerability is triggered when an attacker sends multiple TCP SYN packets with different sequence numbers within the same flow tuple. Suricata's logic for establishing and maintaining session state fails to correctly handle this scenario, resulting in two distinct outcomes depending on the system's operational mode:
- IDS mode: Suricata may fail to pick up the TCP session, leading to a detection and logging bypass. Malicious traffic can traverse the network without being inspected or recorded by Suricata.
- IPS mode: The same flaw causes Suricata to block the entire flow, which can result in denial of service for legitimate connections.
The vulnerability is classified as CWE-358: Improperly Implemented Security Check for Standard. This means Suricata's implementation does not fully conform to the expected TCP session validation and tracking standards, particularly in handling edge cases involving multiple SYN packets with differing sequence numbers.
The root cause is a logic flaw in how Suricata correlates SYN packets and establishes the session state. If the sequence numbers differ, Suricata may not recognize subsequent packets as belonging to the same session, causing it to lose visibility or take incorrect action on the flow. This can be exploited by attackers using packet crafting tools to generate the necessary traffic patterns.
The issue is addressed in Suricata 7.0.12 and 8.0.1, where the TCP session handling logic has been updated to correctly process multiple SYNs with varying sequence numbers within the same flow tuple.
Affected Systems and Versions
- Suricata versions 7.0.11 and below
- Suricata version 8.0.0
Both IDS and IPS configurations are affected. The vulnerability is fixed in 7.0.12 (7.x series) and 8.0.1 (8.x series).
Vendor Security History
The Open Information Security Foundation (OISF) has a strong track record of rapid response to vulnerabilities in Suricata. Previous issues, such as CVE-2021-37592, also involved TCP session handling. OISF routinely releases coordinated patches for multiple supported branches and maintains transparent security advisories. Their security maturity is evident in their public disclosure and patching process.