CVE-2026-31933: 
Suricata vulnerability analysis and mitigation

CVE-2026-31933 is a denial-of-service vulnerability in Suricata, the open-source network IDS, IPS, and NSM engine, caused by quadratic complexity in stream inspection. Specially crafted network traffic can cause Suricata to slow down significantly, degrading performance in IDS mode. All versions prior to 7.0.15 and 8.0.4 (including the 8.0.0–8.0.3 range) are affected. The vulnerability was published on April 2, 2026, with patches released on March 17, 2026 (versions 7.0.15 and 8.0.4). It carries a CVSS v3.1 base score of 7.5 (High) (GitHub Advisory, Red Hat Bugzilla).

The root cause is classified under CWE-407 (Inefficient Algorithmic Complexity) and CWE-770 (Allocation of Resources Without Limits or Throttling), specifically a quadratic-complexity algorithm in Suricata's stream inspection engine. An unauthenticated remote attacker can send specially crafted network traffic that triggers worst-case computational paths during stream reassembly or inspection, causing disproportionate CPU consumption and performance degradation. No authentication, user interaction, or special privileges are required — the attack is executable from the network with low complexity. The vulnerability was discovered by OSS-Fuzz and tracked internally at the Open Information Security Foundation (OISF) under issue #8272 (GitHub Advisory).

Successful exploitation causes Suricata to slow down severely in IDS mode, resulting in a denial-of-service condition that impairs the engine's ability to inspect and detect malicious network traffic. This directly undermines the effectiveness of network security monitoring and threat prevention, potentially allowing other attacks to go undetected during the degradation window. There is no confidentiality or integrity impact; the sole consequence is high availability impact on the Suricata process (GitHub Advisory, Red Hat Bugzilla).

As of the time of reporting, there is no public proof-of-concept exploit and no evidence of active in-the-wild exploitation (Feedly). The vulnerability has an EPSS score of approximately 0.04%, indicating a low probability of exploitation in the near term. The attack requires no authentication and no user interaction, making it trivially executable by any network-adjacent attacker if a PoC were to emerge. The CVE is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

1. Reconnaissance: Identify network segments or hosts running Suricata in IDS mode using passive observation or active scanning for known Suricata deployment patterns (e.g., monitoring interfaces, associated management ports).
2. Craft malicious traffic: Construct specially crafted network streams designed to trigger worst-case quadratic complexity in Suricata's stream inspection engine — for example, fragmented or overlapping TCP streams that maximize reassembly processing overhead.
3. Transmit traffic: Send the crafted traffic toward the monitored network segment so that Suricata's inspection engine processes it. No authentication or special access to the Suricata host is required.
4. Observe degradation: Monitor for signs of Suricata performance degradation (e.g., increased packet drop rates, alert latency, or engine unresponsiveness), confirming successful exploitation and effective blinding of the IDS (GitHub Advisory).

• Process: Suricata process exhibiting sustained high CPU utilization without a corresponding spike in legitimate traffic volume; increased packet drop counters in suricata --dump-counters output.
• Logs: Suricata stats logs showing abnormal stream reassembly queue depths or excessive memory usage; warnings or errors related to stream engine performance in suricata.log.
• Network: Unusual volumes of fragmented, overlapping, or malformed TCP streams targeting monitored interfaces; traffic patterns inconsistent with normal baseline that correlate with performance degradation onset.
• Operational: Sudden increase in missed alerts or detection gaps coinciding with high CPU load on the Suricata host, potentially indicating the IDS is being blinded (GitHub Advisory).

Upgrade Suricata to version 7.0.15 or 8.0.4 (or later), which contain the fix for this vulnerability. The OISF has confirmed no workarounds are available — patching is the only remediation. Organizations running Suricata in critical network security roles should prioritize this update given the high availability impact and ease of exploitation (GitHub Advisory, Suricata Release).

The OISF published the security advisory (GHSA-hvp5-gpr6-j4gp) on March 31, 2026, crediting OSS-Fuzz for discovery, and simultaneously released patched versions 7.0.15 and 8.0.4. Red Hat tracked the issue via Bugzilla (Bug 2454375) and classified it as high severity. OpenSUSE issued a security announcement to its mailing list, and the vulnerability was picked up by standard vulnerability aggregators and security news outlets shortly after public disclosure (GitHub Advisory, Red Hat Bugzilla).