CVE-2024-23839

Executive Summary

CVE-2024-23839 is a critical heap use-after-free vulnerability in Suricata, a widely deployed open-source Network Intrusion Detection System (NIDS), Intrusion Prevention System (IPS), and Network Security Monitoring (NSM) engine. The flaw resides in the handling of HTTP traffic when rulesets utilize the http.request_header or http.response_header keywords. An unauthenticated remote attacker can trigger this vulnerability by sending specially crafted network traffic, leading to a denial of service (DoS) condition via application crash or potentially arbitrary code execution in the context of the Suricata process. The vulnerability affects all versions prior to 7.0.3. The official patch was released in version 7.0.3, and a workaround involves avoiding the use of the vulnerable keywords. No public proof-of-concept (PoC) exploit code is currently available, but the technical details are sufficient for a skilled attacker to develop one.

Supply Chain & Package Security

Suricata is distributed as a source tarball, via package managers (e.g., apt, yum), and as a Docker container. Organizations using Suricata in their security stack should treat this as a high-priority supply chain risk. The vulnerability is in the core engine, not a third-party library, so the attack surface is directly within the Suricata binary. Ensure that any deployment, including those in CI/CD pipelines or containerized environments, is updated to version 7.0.3 or later.

CVSS Breakdown & Threat Level

• CVSS Score: 7.1 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector (AV): Network (N) – The vulnerability is exploitable remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required; the attacker only needs to send crafted traffic.
• Privileges Required (PR): None (N) – No authentication is needed.
• User Interaction (UI): None (N) – No user action is required.
• Scope (S): Unchanged (U) – The impact is confined to the vulnerable component.
• Confidentiality (C): None (N) – No data disclosure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – The vulnerability can cause a complete denial of service.

Threat Level: High. The low attack complexity and network-based vector make this a serious threat for any organization running an unpatched Suricata instance with rules that use the vulnerable keywords.

Deep Dive & Mechanics

The vulnerability is a heap use-after-free (UAF) condition in Suricata's HTTP parser. When a rule uses http.request_header or http.response_header, the engine processes HTTP headers and stores them in a heap-allocated buffer. Under specific conditions, crafted traffic can cause the engine to free this buffer prematurely while a pointer to it is still retained. Subsequent access to this freed memory leads to a use-after-free.

Technical Flow:

1. Suricata receives an HTTP request or response.
2. The HTTP parser allocates a heap buffer to store header data.
3. A rule with http.request_header or http.response_header triggers a lookup.
4. Due to a race condition or improper state management, the buffer is freed (e.g., during a connection reset or error handling).
5. The pointer to the freed buffer is still used for header inspection.
6. This results in reading or writing to freed heap memory, causing a crash or potential code execution.

The vulnerability is triggered by specially crafted traffic that exploits the timing or state machine of the HTTP parser. The exact trigger conditions are not publicly documented, but the patch in 7.0.3 addresses the root cause by ensuring proper reference counting or buffer lifecycle management.

Vulnerable vs. Patched Code

The vulnerable code is in the HTTP header handling routines. The patch in version 7.0.3 introduces a fix that prevents the premature free of the header buffer.

Vulnerable Code (Conceptual):

// In http_header.c
void process_header(HttpHeader *hdr) {
    // ... some processing ...
    if (some_error_condition) {
        free(hdr->buffer);  // Buffer freed prematurely
    }
    // Later, hdr->buffer is still used
    inspect_header(hdr->buffer);  // Use-after-free
}

Patched Code (Conceptual):

// In http_header.c
void process_header(HttpHeader *hdr) {
    // ... some processing ...
    if (some_error_condition) {
        // Mark buffer as invalid, but do not free yet
        hdr->buffer_invalid = 1;
    }
    // Check validity before use
    if (!hdr->buffer_invalid) {
        inspect_header(hdr->buffer);
    }
    // Free buffer only when no references remain
    free_header(hdr);
}

The actual patch involves changes to the memory management of HTTP header structures, ensuring that buffers are not freed while still referenced by inspection routines.

Exploitation & Lab Setup

Red Team

Objective: Trigger a denial of service (DoS) on a vulnerable Suricata instance.

Prerequisites:

• A target running Suricata < 7.0.3 with rules using http.request_header or http.response_header.
• Network access to the Suricata monitoring interface.

Exploitation Steps:

1. Identify Target: Scan for Suricata instances (e.g., using Shodan dorks: "suricata http.request_header").
2. Craft Malicious Traffic: Send specially crafted HTTP requests/responses that trigger the UAF. The exact payload is not publicly available, but it likely involves:
   • Sending a partial HTTP request followed by a connection reset.
   • Sending HTTP headers with specific patterns that cause the parser to enter an error state.
   • Exploiting race conditions by sending multiple requests in quick succession.
3. Execute Attack: Use a tool like scapy or a custom Python script to send the crafted traffic.
4. Observe Impact: Monitor the Suricata process for crashes or unresponsiveness.

Example Python Script (Hypothetical):

import socket

def trigger_uaf(target_ip, target_port):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect((target_ip, target_port))
    # Send a partial HTTP request to trigger the vulnerability
    payload = b"GET / HTTP/1.1\r\nHost: example.com\r\nX-Custom: " + b"A" * 1000
    sock.send(payload)
    # Reset the connection to trigger the free
    sock.settimeout(0.1)
    try:
        sock.recv(1024)
    except:
        pass
    sock.close()

# Usage
trigger_uaf("192.168.1.100", 80)

Note: This is a conceptual example. The actual exploit requires reverse engineering the specific trigger conditions.

Blue Team

Detection:

• Monitor Suricata logs for crashes or segmentation faults.
• Use the detection rules provided in the Detection Engineering section.
• Enable Suricata's built-in profiling and debugging to identify abnormal memory access patterns.

Mitigation:

• Immediately upgrade to Suricata 7.0.3 or later.
• If upgrade is not possible, remove or modify rules that use http.request_header or http.response_header.
• Implement network segmentation to limit exposure of Suricata instances.
• Use a Web Application Firewall (WAF) to filter malicious HTTP traffic before it reaches Suricata.

Hunting:

• Search for Suricata processes that have crashed repeatedly.
• Analyze network traffic for patterns that match the hypothetical exploit (e.g., partial HTTP requests followed by resets).
• Review Suricata's stats.log for anomalies in HTTP parser statistics.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Unusual HTTP requests with incomplete headers followed by TCP RST packets.
  • High volume of HTTP traffic targeting Suricata's monitoring interface.
  • Repeated connection resets from the same source IP.

• Host IOCs:

  • Suricata process crashes (segmentation faults) recorded in system logs.
  • Core dump files generated by Suricata.
  • Abnormal memory usage patterns in Suricata (e.g., rapid allocation/deallocation).

• File IOCs:

  • Suricata log entries containing "use-after-free" or "heap corruption" errors.
  • Modified Suricata configuration files that remove vulnerable keywords.

Detection Engineering

YARA Rule

rule CVE_2024_23839_Suricata_Heap_UAF {
    meta:
        description = "Detects Suricata heap use-after-free vulnerability CVE-2024-23839"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-23839"
        hash = "d41d8cd98f00b204e9800998ecf8427e"
    strings:
        $s1 = "http.request_header" ascii wide nocase
        $s2 = "http.response_header" ascii wide nocase
        $s3 = "7.0.3" ascii wide
    condition:
        (uint16(0) == 0x4d5a or uint32(0) == 0x464c457f) and
        ($s1 or $s2) and
        not $s3
}

Sigma Rule

title: Suricata Heap Use-After-Free Exploitation Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects network traffic patterns associated with CVE-2024-23839 exploitation
author: Valters IT
date: 2024/01/01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-23839
logsource:
    category: network_connection
    product: suricata
detection:
    selection:
        event_type: alert
        alert.signature_id: 202423839
    condition: selection
falsepositives:
    - Legitimate HTTP traffic with unusual headers
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-23839 - Potential Heap Use-After-Free Exploit"; flow:to_server; content:"http.request_header"; http_header_names; sid:202423839; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Suricata: Update to version 7.0.3 or later. This is the only complete fix.

   # For Debian/Ubuntu
   sudo apt-get update && sudo apt-get install suricata=1:7.0.3-1
   # For RHEL/CentOS
   sudo yum update suricata
   # For source compilation
   wget https://www.openinfosecfoundation.org/download/suricata-7.0.3.tar.gz
   tar -xzf suricata-7.0.3.tar.gz
   cd suricata-7.0.3
   ./configure && make && sudo make install
   

2. Workaround: If upgrade is not immediately possible, remove or comment out any rules that use http.request_header or http.response_header keywords.

   # Example: Comment out rules in /etc/suricata/rules/local.rules
   # alert http any any -> any any (msg:"Example rule"; http.request_header; sid:1000001;)
   

3. Restart Suricata: After applying changes, restart the Suricata service.

   sudo systemctl restart suricata
   

Long-Term Measures:

• Implement a vulnerability management program to ensure timely patching of security tools.
• Use network segmentation to isolate Suricata instances from untrusted networks.
• Deploy a Web Application Firewall (WAF) as an additional layer of defense.
• Regularly review and update Suricata rulesets to minimize the use of vulnerable keywords.
• Monitor Suricata's official GitHub repository and mailing lists for security advisories.

Valters IT