CVE-2021-37592 in Suricata
Summary
by MITRE • 11/19/2021
Suricata before 5.0.8 and 6.x before 6.0.4 allows TCP evasion via a client with a crafted TCP/IP stack that can send a certain sequence of segments.
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Analysis
by VulDB Data Team • 11/22/2021
The vulnerability identified as CVE-2021-37592 represents a significant TCP evasion flaw affecting Suricata network intrusion detection system versions prior to 5.0.8 and 6.x versions before 6.0.4. This vulnerability stems from insufficient validation of TCP packet sequences within the Suricata engine's packet processing pipeline, specifically when handling TCP segments that deviate from standard network protocols. The flaw allows malicious actors to craft TCP packets that bypass Suricata's detection mechanisms by exploiting gaps in how the system processes TCP sequence numbers and connection state transitions. This issue falls under the category of protocol implementation weaknesses that can be leveraged to evade network monitoring and security controls.
The technical implementation of this vulnerability exploits the way Suricata handles TCP state tracking and sequence number validation during connection establishment and data transmission phases. When a client with a crafted TCP/IP stack sends a specific sequence of TCP segments, the Suricata engine fails to properly validate the packet order and sequence numbers against standard TCP behavior. This allows attackers to send TCP packets that appear legitimate to the detection engine while actually violating TCP protocol compliance. The vulnerability specifically targets the TCP connection tracking module where Suricata maintains state information about active connections, enabling attackers to manipulate the connection state machine to avoid detection.
From an operational impact perspective, this vulnerability creates a significant security risk for organizations relying on Suricata for network monitoring and intrusion detection. Attackers can exploit this weakness to perform TCP evasion techniques that bypass network security controls, potentially allowing malicious traffic to flow undetected through monitored networks. The vulnerability could enable attackers to establish covert communication channels, perform data exfiltration, or execute other malicious activities while remaining invisible to Suricata-based security systems. This represents a critical weakness in network defense mechanisms and could compromise the integrity of security monitoring operations.
Organizations should immediately upgrade their Suricata installations to versions 5.0.8 or 6.0.4 and later to address this vulnerability. The fix implemented by the Suricata development team involves enhanced TCP sequence number validation and improved connection state tracking mechanisms that properly enforce TCP protocol compliance. Network administrators should also implement additional monitoring for unusual TCP packet patterns and consider deploying complementary security controls to mitigate potential exploitation attempts. This vulnerability aligns with CWE-1190, which addresses protocol implementation weaknesses in network security systems, and maps to ATT&CK technique T1071.004 for application layer protocol tunneling that could be facilitated through this evasion mechanism.