CVE-2026-71855 in Suricata
Summary
by MITRE • 09/19/2026
Suricata is a network Intrusion Detection System, Intrusion Prevention System and Network Security Monitoring engine. Prior to 7.0.17 and 8.0.6, src/flow-hash.c can treat an IPv4 and IPv6 flow as equal without comparing the IP family when their raw address words, ports, protocol, VLAN, recursion level, live device, and hash bucket align. An IPv6 packet can therefore reuse IPv4 flow state or the reverse, causing incorrect flowbit state, detection bypass, or IP-only bypass. This issue is fixed in versions 8.0.6 and 7.0.17.
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Analysis
by VulDB Data Team • 09/19/2026
Suricata serves as a critical component in modern network security architectures, functioning simultaneously as an Intrusion Detection System, an Intrusion Prevention System, and a Network Security Monitoring engine. Its effectiveness relies heavily on the accurate identification and tracking of network flows to correlate packets into coherent sessions for deep packet inspection and rule-based detection. The vulnerability identified within versions prior to 7.0.17 and 8.0.6 resides in the flow hashing mechanism located in the source file src/flow-hash.c, which is responsible for assigning incoming traffic to specific flow buckets for state tracking. This component failed to adequately distinguish between different IP protocol families during the hash computation process, creating a significant logical flaw that undermines the integrity of session management.
The technical root cause of this vulnerability lies in the comparison logic used when determining if two network flows are identical or should share the same hash bucket. Specifically, the implementation treated an IPv4 flow and an IPv6 flow as equal if their raw address words, source and destination ports, protocol type, VLAN identifiers, recursion levels, live device indices, and resulting hash buckets aligned perfectly. Crucially, the code omitted a check for the IP family itself during this equality assessment. This oversight means that the system did not verify whether the underlying network layer was using IPv4 or IPv6 before concluding that two flows were equivalent. Consequently, an attacker could craft packets where the numerical values of addresses and ports coincidentally matched those of an existing flow, despite being in a different IP version space.
The operational impact of this flaw is substantial for any organization relying on Suricata for security monitoring and prevention. Because IPv6 packets can reuse the state information allocated to IPv4 flows, or vice versa, the engine may apply detection rules intended for one protocol family to traffic from another without proper validation. This leads directly to incorrect flowbit states, which are internal flags used by Suricata to track session progress and trigger specific actions. More critically, this confusion enables a bypass of security controls. An attacker could potentially evade intrusion prevention signatures or access control lists designed for IPv4 by sending malicious payloads via IPv6 that map to the same flow state as legitimate IPv4 traffic. This results in detection bypasses where malicious activity goes unnoticed because it is incorrectly associated with a benign, pre-existing session context.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-841 Improper Enforcement of Flow Rules. The failure to validate the IP family constitutes an input validation error that allows for flow rule enforcement bypasses. In terms of tactical mapping within the MITRE ATT&CK framework, this issue facilitates techniques related to Defense Evasion, specifically those involving protocol confusion or tunneling to avoid detection by security monitoring tools. By exploiting the ambiguity in flow identification, adversaries can mask their activities behind legitimate-looking session states, making it significantly harder for analysts to distinguish between normal traffic and malicious exploitation attempts.
To mitigate this risk, organizations running Suricata must ensure they are operating on version 8.0.6 or later, or version 7.0.17 and above, where the flow hash logic has been corrected to explicitly compare IP families before determining flow equality. This patch ensures that IPv4 and IPv6 flows remain strictly segregated in their state tracking mechanisms, preventing cross-protocol state reuse. Administrators should also review their network segmentation policies to ensure that any legacy systems or dual-stack configurations are properly monitored for anomalies that might indicate exploitation attempts against this specific logic flaw before the update is applied. Regular updates of intrusion detection and prevention system engines remain essential to maintain visibility into evolving attack vectors that exploit logical inconsistencies in protocol handling.