Executive Intelligence Brief

A critical type confusion vulnerability (CVE-2026-94083) has been discovered in Suricata, a widely-used network intrusion detection and prevention system. This vulnerability, with a CVSS score of 9.4, can lead to an invalid free operation, potentially causing a denial-of-service (DoS) or remote code execution. The vulnerability affects Suricata versions before 8.0.7 and is triggered when the app-layer.protocols.doh2 is enabled, which is the default setting in Suricata 8.x versions. Immediate patching is recommended to mitigate this critical threat.

Threat Overview

Suricata is an open-source network intrusion detection and prevention system (IDS/IPS) used for real-time network traffic inspection and security monitoring. It is widely deployed in various environments to detect and prevent cyber threats. The vulnerability, CVE-2026-94083, affects Suricata versions before 8.0.7. This vulnerability is caused by a type confusion issue in the DoH2 (DNS over HTTPS 2) protocol handling, which can lead to an invalid free operation. This occurs because the cleanup code for the HTTP2 state is executed even when the actual state is HTTP1, during a DoH2 request with an HTTP1 to HTTP2 upgrade.

Technical Deep Dive

Vulnerability Classification

The vulnerability is classified as CWE-843: Type Confusion. Type confusion vulnerabilities occur when a variable, object, or data structure is used in an unintended way, often due to incorrect type checking or improper handling of different data types. In this case, the type confusion happens in the DoH2 protocol handling, leading to incorrect state management and an invalid free operation.

Root Cause Analysis

The root cause of this vulnerability is the improper handling of the HTTP2 state during a DoH2 request with an HTTP1 to HTTP2 upgrade. Specifically, the cleanup code for the HTTP2 state is executed even though the actual state is HTTP1. This mismatch causes an invalid free operation, which can lead to a denial-of-service (DoS) or potentially allow for remote code execution.

Attack Vector & Chain

The attack vector for this vulnerability is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U, indicating that the attack can be launched remotely, requires low attack complexity, does not require any privileges, and does not require user interaction. The scope of the vulnerability is unchanged, meaning the vulnerable component is not able to affect other components.

Exploitation Scenario Walkthrough

Scenario: Remote DoS via Type Confusion in Suricata

Reconnaissance: An attacker scans for Suricata instances, particularly those running versions before 8.0.7, using network scanning tools like Nmap or Shodan.

Weaponization: The attacker crafts a malicious DoH2 request that triggers the type confusion vulnerability, causing an HTTP1 to HTTP2 upgrade.

Delivery & Exploitation: The attacker sends the crafted DoH2 request to the Suricata instance. The Suricata instance, processing the request, incorrectly executes the cleanup code for the HTTP2 state, leading to an invalid free operation.

Post-Exploitation: The attacker may leverage the denial-of-service condition to disrupt network security monitoring and potentially gain an advantage for further attacks.

Impact Realization: The final impact is a denial-of-service condition, potentially allowing the attacker to evade detection or disrupt security operations.

Exploitation in the Wild

There is no indication that this vulnerability is currently being actively exploited in the wild. However, given its critical severity and remote attack vector, there is a high likelihood that attackers will target this vulnerability if not promptly patched.

Impact Analysis

Direct Impact

The direct impact of this vulnerability is a denial-of-service (DoS) condition, potentially leading to a remote code execution. The CVSS score of 9.4 indicates a critical severity, with high impacts on confidentiality and integrity, and a low impact on availability.

Downstream & Cascading Effects

The downstream effects of this vulnerability include potential disruptions to network security monitoring and incident response capabilities. If exploited, this vulnerability could allow attackers to evade detection or disrupt security operations, potentially leading to further attacks.

Affected Products & Versions

The vulnerability affects Suricata versions before 8.0.7. Specifically:

  • Vendor: OISF
  • Product: Suricata
  • Affected versions: 8.0.0 to 8.0.6

The fixed version is Suricata 8.0.7.

Detection & Threat Hunting

Indicators of Compromise

No specific indicators of compromise (IoCs) are provided in the source data. However, network traffic logs and Suricata instance logs should be monitored for suspicious DoH2 requests or signs of denial-of-service conditions.

Detection Rules & Signatures

Detection logic may include monitoring for unusual DoH2 protocol activity, particularly requests that trigger HTTP1 to HTTP2 upgrades. Relevant log sources include network traffic logs and Suricata instance logs. Behavioral patterns indicating exploitation may include:

  • Unusual spikes in DoH2 traffic
  • Signs of invalid free operations in Suricata logs
  • Denial-of-service conditions affecting network security monitoring

Threat Hunting Queries

Threat hunting queries may include searching for:

  • Suspicious DoH2 requests in network traffic logs
  • Unusual patterns in Suricata instance logs
  • Signs of denial-of-service conditions affecting network security monitoring

Remediation & Hardening

Immediate Actions (0-24 hours)

1. **Patch Suricata to version 8.0.7 or later.

2. Ensure that app-layer.protocols.doh2 is not unnecessarily enabled if not required.

Short-Term Hardening (1-7 days)

1. **Implement network segmentation** to limit the spread of potential attacks.

2. **Enhance monitoring** for suspicious DoH2 protocol activity.

3. **Restrict access** to Suricata instances to minimize the attack surface.

Strategic Recommendations

1. **Regularly update and patch** Suricata and other network security tools.

2. **Implement a robust security monitoring** program to detect and respond to threats.

3. **Conduct regular vulnerability assessments** to identify and address potential weaknesses.

Analyst Assessment

The critical severity of this vulnerability, combined with its remote attack vector and potential for denial-of-service or remote code execution, makes it a high-priority threat. Organizations should immediately patch Suricata instances to version 8.0.7 or later to mitigate this threat. The likelihood of exploitation is high due to the vulnerability's characteristics and the potential benefits to attackers.

Sources