CVE-2024-23836 - How a Simple Exploit Could Crash Suricata IDS

Suricata is a powerful open-source tool used for network intrusion detection, prevention, and monitoring. With its wide adoption in enterprise and research environments, keeping it secure is critical. In early 2024, a new vulnerability, CVE-2024-23836, was discovered, affecting many Suricata users worldwide. If left unpatched, attackers can exploit this flaw to slow down or even crash your entire intrusion detection system. In this long read, we’ll break down this vulnerability in plain English: what it is, how it works, exploit example, patch details, and—most importantly—how you can protect your network.

Affected Software: Suricata (before versions 6..16 and 7..3)

- Vulnerability Type: Denial of Service (DoS) via resource exhaustion (CPU/Memory)

Vulnerability Overview

Suricata uses "app-layer parsers" to analyze different layers of network traffic. Before the recent patches, certain traffic patterns—carefully crafted by an attacker—could force Suricata to spend a lot more CPU cycles and memory processing them than intended. This means an attacker doesn’t need to break into your system; they just need to send a bunch of crafted packets, and Suricata may grind to a halt.

Quote from the official advisory

> “An attacker can craft traffic that causes Suricata to use far more CPU and memory for processing the traffic than needed, leading to extreme slow downs and denial of service.”
> — NCSC-NL advisory

How Does the Exploit Work?

The vulnerability centers around Suricata’s parsing of certain protocols at the application layer. By crafting unusual or malformed packets, attackers can force Suricata to keep re-assembling and analyzing the same or unusual flows multiple times. Each iteration uses CPU and memory, and with enough requests, Suricata simply runs out of resources.

Example Attack

Step 1: Attacker sends a flood of specially crafted packets targeting an enabled app-layer parser (e.g., HTTP, SMB, DNS).

Step 2: Suricata’s affected code keeps re-parsing these packets and trying to reassemble streams.

Step 3: CPU load spikes, memory usage soars—eventually, the Suricata process becomes unresponsive.

Result: A full Denial of Service for network detection or prevention, leaving your network blind.

Sample Exploit Snippet

Below is a simplified Python script example that illustrates the concept of flooding Suricata with crafted TCP packets to abuse its stream reassembly routines. Note: This is for educational purposes only.

import socket
import time

target_ip = "192.168.1.100"  # Suricata sensor IP
target_port = 80  # Target service (e.g., HTTP parser enabled)

payload = b"A" * 4096  # Large, abnormal payload

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

for _ in range(50000):  # Large number of requests in fast succession
    try:
        sock.connect((target_ip, target_port))
        sock.send(payload)
        sock.close()
    except Exception as e:
        pass
    time.sleep(.01)  # Tiny delay to keep connections open

By running a tool like this from multiple attacker-controlled sources, you can initiate a distributed DoS that can overwhelm Suricata on unpatched versions.

Download the updated version

- Suricata downloads

The patched versions include improvements in the app-layer stream parsing and resource management, making it far harder for an attacker to exhaust resources with crafted traffic.

1. Disable Vulnerable Protocol Parsers

In the suricata.yaml file, find the app-layer protocols you don’t need or suspect are at risk, and disable their parsers. For example:

app-layer:
  protocols:
    http:
      enabled: no
    smb:
      enabled: no

2. Adjust stream.reassembly.depth

This value controls how much data Suricata will reassemble in streams. Reducing it minimizes the damage an attacker can do.

Example

stream:
  reassembly:
    depth: 512kb  # Reduce from higher default values

References and Further Reading

- Suricata security advisory for CVE-2024-23836
- Suricata Release Notes
- Official Suricata Documentation

[ ] Lower reassembly depth to reduce impact

Bottom line:
CVE-2024-23836 is a critical reminder that even leading open-source security tools can be taken down with carefully crafted traffic. Patch promptly, tweak your configs, and review which protocols you truly need to monitor—don’t give attackers an easy way to blind your defenses!

*This post is exclusive and purpose-written for educational value. Reuse only with attribution.*

Timeline

Published on: 02/26/2024 16:27:57 UTC
Last modified on: 03/07/2024 03:15:06 UTC