CVE-2026-31933: Suricata IDS/IPS DoS Vulnerability

CVE-2026-31933 Overview

CVE-2026-31933 is an algorithmic complexity attack vulnerability affecting Suricata, the widely-deployed open-source network Intrusion Detection System (IDS), Intrusion Prevention System (IPS), and Network Security Monitoring (NSM) engine. Prior to versions 7.0.15 and 8.0.4, specially crafted network traffic can cause Suricata to experience significant performance degradation when operating in IDS mode.

This vulnerability, classified under CWE-407 (Inefficient Algorithmic Complexity), allows remote unauthenticated attackers to send malicious traffic patterns that trigger computationally expensive operations within the Suricata engine, effectively causing a denial of service condition through resource exhaustion.

Critical Impact

Remote attackers can degrade Suricata IDS performance through specially crafted traffic, potentially allowing malicious activity to evade detection during the slowdown period.

Affected Products

• Suricata versions prior to 7.0.15
• Suricata versions prior to 8.0.4
• Suricata IDS/IPS/NSM deployments in IDS mode

Discovery Timeline

• April 2, 2026 - CVE-2026-31933 published to NVD
• April 2, 2026 - Last updated in NVD database

Technical Details for CVE-2026-31933

Vulnerability Analysis

This vulnerability exploits inefficient algorithmic complexity within Suricata's traffic processing pipeline. When the engine encounters specially crafted packets or traffic patterns, it triggers worst-case algorithmic behavior that consumes excessive CPU cycles. The attack can be executed remotely across the network without requiring any authentication or user interaction.

The impact is limited to availability, with no direct effect on confidentiality or integrity. However, the performance degradation in IDS mode is particularly concerning as it may allow attackers to slip malicious traffic past detection systems during periods of slowdown, effectively creating a window for undetected attacks.

Organizations relying on Suricata for network security monitoring should prioritize patching, as the vulnerability enables attackers to undermine the very systems designed to protect network infrastructure.

Root Cause

The root cause is classified under CWE-407: Inefficient Algorithmic Complexity. This occurs when an algorithm's computational complexity allows an attacker to craft inputs that trigger worst-case performance characteristics. In Suricata's case, certain traffic patterns cause the processing engine to consume disproportionate resources relative to the input size.

This type of vulnerability is particularly insidious in security monitoring tools, as attackers can use it to blind defenders while conducting other malicious activities on the network.

Attack Vector

The attack is network-based and requires no privileges or user interaction. An attacker can send specially crafted packets to a network segment monitored by a vulnerable Suricata instance. The malicious traffic triggers algorithmic inefficiencies within the IDS processing pipeline, causing performance degradation.

The attack scenario involves:

1. Attacker identifies a network protected by Suricata IDS
2. Specially crafted traffic is sent to the monitored network segment
3. Suricata's processing engine slows down due to algorithmic complexity issues
4. Detection capabilities are degraded during the slowdown
5. Attacker may use this window to conduct further malicious activities undetected

Technical details regarding the specific traffic patterns and affected code paths are available in the GitHub Security Advisory and OISF Issue #8272.

Detection Methods for CVE-2026-31933

Indicators of Compromise

• Unusual CPU spikes on Suricata sensor nodes without corresponding increases in legitimate traffic volume
• Increased packet drop rates or processing delays in Suricata statistics
• Anomalous traffic patterns with characteristics designed to trigger algorithmic complexity
• Performance degradation alerts from network monitoring systems overseeing Suricata instances

Detection Strategies

• Monitor Suricata performance metrics including CPU utilization, packet processing rates, and drop statistics
• Implement baseline monitoring for normal Suricata operation and alert on significant deviations
• Deploy network traffic analysis to identify patterns associated with algorithmic complexity attacks
• Review Suricata logs for performance anomalies correlated with specific traffic sources

Monitoring Recommendations

• Configure alerting thresholds for Suricata CPU utilization exceeding normal operational baselines
• Monitor stats.log output for increased drop rates and processing delays
• Implement external health checks to verify Suricata responsiveness during peak traffic periods
• Consider deploying redundant IDS sensors to maintain coverage during potential attack windows

How to Mitigate CVE-2026-31933

Immediate Actions Required

• Upgrade Suricata to version 7.0.15 or later for 7.x branch deployments
• Upgrade Suricata to version 8.0.4 or later for 8.x branch deployments
• Review current Suricata version across all network security monitoring infrastructure
• Implement additional monitoring for IDS performance during the upgrade window
• Consider temporary deployment of supplementary detection mechanisms during vulnerability window

Patch Information

The Open Information Security Foundation (OISF) has released patched versions addressing this vulnerability. Organizations should upgrade to the following versions:

• Suricata 7.x branch: Upgrade to version 7.0.15 or later
• Suricata 8.x branch: Upgrade to version 8.0.4 or later

For detailed patch information and upgrade instructions, refer to the GitHub Security Advisory.

Workarounds

• Implement network-level rate limiting to reduce the impact of potential attack traffic
• Deploy additional IDS sensors in parallel to maintain detection capability during performance degradation
• Configure resource limits for Suricata processes to prevent complete system exhaustion
• Implement traffic filtering at network perimeter to block known malicious sources

# Example: Check current Suricata version
suricata --build-info | grep -i version

# Example: Update Suricata on Debian/Ubuntu systems
sudo apt update
sudo apt install suricata

# Verify the updated version meets minimum requirements
suricata -V