CVE-2025-42604

Executive Summary

CVE-2025-42604 exposes a critical information disclosure vulnerability in Meon KYC solutions. The debug mode is enabled on certain API endpoints, allowing a remote attacker to access unauthorized endpoints and receive detailed error messages. This leakage can reveal system internals, configuration paths, database schemas, or other sensitive data, aiding further attacks. No patch or exploit code is currently available; the vendor has not confirmed a fix.

Supply Chain & Package Security

This vulnerability is not related to an open-source package (NPM, PyPI, Go, Ruby). It affects a proprietary KYC solution from Meon. Supply chain risk is limited to the vendor’s own software distribution.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official vector assigned)
• Attack Vector (AV): Network (likely)
• Attack Complexity (AC): Low (debug endpoints often require no authentication)
• Privileges Required (PR): None
• User Interaction (UI): None
• Scope (S): Unchanged
• Confidentiality (C): High (system information disclosure)
• Integrity (I): None
• Availability (A): None
• Threat Level: Medium (information leakage can enable privilege escalation or lateral movement)

Deep Dive & Mechanics

The vulnerability stems from debug mode being enabled in production API endpoints. When an attacker sends malformed or unexpected requests to these endpoints, the server returns verbose error messages containing stack traces, file paths, database queries, or environment variables. This is a classic information disclosure (CWE-200) that violates the principle of least information.

Root Cause: The application’s configuration does not disable debug output in production. The API framework (likely a common web framework) is set to debug=True or equivalent, causing detailed error pages to be returned instead of generic error messages.

Attack Vector: An attacker can enumerate API endpoints (e.g., /api/v1/kyc/verify, /api/v1/user/details) and send invalid data (e.g., missing parameters, invalid JSON, SQL injection attempts) to trigger error responses. The debug output reveals internal paths, database table names, or API keys.

Impact: An attacker can map the internal architecture, discover other endpoints, and potentially find more severe vulnerabilities (e.g., SQL injection, authentication bypass) using the leaked information.

Vulnerable vs. Patched Code

Since no patch is available, we compare the vulnerable behavior to a secure configuration.

Vulnerable (debug mode enabled):

# Example Flask app with debug=True
from flask import Flask, request, jsonify
app = Flask(__name__)
app.config['DEBUG'] = True  # Vulnerable

@app.route('/api/v1/kyc/verify', methods=['POST'])
def verify_kyc():
    data = request.get_json()
    # Missing validation
    result = process_kyc(data)
    return jsonify(result)

When an invalid request is sent, Flask returns a full stack trace with environment variables.

Patched (debug mode disabled):

from flask import Flask, request, jsonify
app = Flask(__name__)
app.config['DEBUG'] = False  # Patched

@app.route('/api/v1/kyc/verify', methods=['POST'])
def verify_kyc():
    data = request.get_json()
    if not data:
        return jsonify({'error': 'Invalid request'}), 400
    result = process_kyc(data)
    return jsonify(result)

The patched version returns a generic error message and logs details server-side only.

Exploitation & Lab Setup

Red Team (Attacker)

Objective: Extract system information from Meon KYC API endpoints.

Lab Setup:

1. Identify target API endpoints (e.g., via Shodan dork: "Meon KYC").
2. Use Burp Suite or curl to send malformed requests.

Exploitation Steps:

# Trigger a 500 error by sending invalid JSON
curl -X POST https://target.com/api/v1/kyc/verify \
  -H "Content-Type: application/json" \
  -d 'invalid json'

# Trigger a missing parameter error
curl -X POST https://target.com/api/v1/kyc/verify \
  -H "Content-Type: application/json" \
  -d '{}'

# Attempt SQL injection to see database error
curl -X POST https://target.com/api/v1/kyc/verify \
  -H "Content-Type: application/json" \
  -d '{"user_id": "1 OR 1=1"}'

Expected Output: The server returns a detailed error message with stack trace, file paths, and possibly database credentials.

Blue Team (Defender)

Detection: Monitor for error responses with status codes 500 and large response bodies containing stack traces.

Mitigation:

• Disable debug mode in production.
• Implement generic error handlers.
• Use a Web Application Firewall (WAF) to block malformed requests.
• Log errors server-side only.

Hunting Query (Splunk):

index=web sourcetype=access_combined
status=500
| search response_body="*Traceback*" OR response_body="*File *"
| table _time, src_ip, uri, response_body

Indicators of Compromise (IOCs)

• Network: HTTP responses with status 500 and body containing Traceback, File, line, Error, or Exception.
• Endpoints: Any API endpoint returning verbose error messages (e.g., /api/v1/kyc/verify, /api/v1/user/details).
• Logs: Server logs showing repeated malformed requests to API endpoints.

Detection Engineering

YARA Rule

rule Detect_Meon_Debug_Error {
    meta:
        description = "Detects verbose error messages from Meon KYC API debug mode"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-42604"
    strings:
        $traceback = "Traceback (most recent call last)" nocase
        $filepath = /[A-Za-z]:\\[^\\]+\\[^\\]+\.py/  // Windows path
        $filepath2 = /\/[a-z]+\/[a-z]+\/[a-z]+\.py/  // Unix path
        $error_msg = "Error" nocase
        $exception = "Exception" nocase
    condition:
        any of ($traceback, $filepath, $filepath2) and ($error_msg or $exception)
}

Sigma Rule

title: Meon KYC Debug Error Response
id: 9b1c2d3e-4f5a-6b7c-8d9e-0f1a2b3c4d5e
status: experimental
description: Detects HTTP 500 responses with verbose error messages from Meon KYC API
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        sc-status: 500
        response_body|contains:
            - 'Traceback'
            - 'File "'
            - 'Error'
            - 'Exception'
    condition: selection
falsepositives:
    - Legitimate debugging during development
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-42604 Meon KYC Debug Error Response";
    flow:to_server,established;
    content:"HTTP/1.1 500"; http_stat_code;
    content:"Traceback"; http_server_body;
    content:"File"; http_server_body;
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

1. Immediate: Disable debug mode in production configuration. Set DEBUG=False or equivalent in the application framework.
2. Short-term: Implement custom error handlers that return generic messages (e.g., {"error": "Internal server error"}) and log full details server-side.
3. Long-term: Conduct a security audit of all API endpoints to ensure no sensitive data is leaked in any response.
4. Monitoring: Deploy the YARA/Sigma/Suricata rules above to detect exploitation attempts.
5. Vendor Contact: Reach out to Meon for an official patch or advisory.

Valters IT
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