CVE-2024-3676

Executive Summary

CVE-2024-3676 is an Improper Input Validation vulnerability in the Proofpoint Encryption endpoint of Proofpoint Enterprise Protection. An unauthenticated remote attacker can send a specially crafted HTTP request to create additional Encryption user accounts under the attacker’s control. These accounts can then send spoofed email to any user within domains configured by the administrator. The vulnerability has a CVSS score of 7.5 (High) due to the lack of authentication required and the potential for email spoofing and account creation. No public exploit code or patch is currently available.

Supply Chain & Package Security

This vulnerability is not related to an open-source package (NPM, PyPI, Go, Ruby) but affects a proprietary enterprise security product. Supply chain risk is limited to the product’s deployment and configuration.

CVSS Breakdown & Threat Level

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

The threat level is High due to the ease of exploitation and the potential for widespread email spoofing and account takeover.

Deep Dive & Mechanics

The vulnerability resides in the Proofpoint Encryption endpoint, which is responsible for creating and managing encryption user accounts. The endpoint fails to properly validate input in HTTP requests, allowing an attacker to craft a request that creates new user accounts without proper authorization. These accounts are then able to send emails that appear to come from legitimate users within the organization’s domains.

Root Cause: The endpoint does not enforce authentication or authorization checks before processing account creation requests. Additionally, input validation is insufficient to prevent the injection of malicious parameters.

Attack Flow:

1. Attacker identifies the Proofpoint Encryption endpoint (e.g., /encryption/api/v1/users).
2. Attacker sends a POST request with crafted JSON payload containing attacker-controlled email addresses and domain names.
3. The endpoint creates new user accounts without verifying the requester’s identity.
4. Attacker uses these accounts to send spoofed emails to any user in the configured domains.

Vulnerable vs. Patched Code

No patch is currently available. The vulnerable code likely lacks authentication checks and input sanitization. A patched version would require:

• Authentication (e.g., API key or session token) for account creation.
• Input validation to ensure only authorized domains and email addresses are used.
• Rate limiting to prevent abuse.

Vulnerable Code (Conceptual):

@app.route('/encryption/api/v1/users', methods=['POST'])
def create_user():
    data = request.get_json()
    email = data['email']
    domain = data['domain']
    # No authentication or validation
    user = User(email=email, domain=domain)
    db.session.add(user)
    db.session.commit()
    return jsonify({"status": "created"}), 201

Patched Code (Conceptual):

@app.route('/encryption/api/v1/users', methods=['POST'])
@require_auth
def create_user():
    data = request.get_json()
    email = data['email']
    domain = data['domain']
    if not is_valid_domain(domain) or not is_authorized_domain(domain):
        return jsonify({"error": "Unauthorized domain"}), 403
    if not is_valid_email(email):
        return jsonify({"error": "Invalid email"}), 400
    user = User(email=email, domain=domain)
    db.session.add(user)
    db.session.commit()
    return jsonify({"status": "created"}), 201

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to the Proofpoint Encryption endpoint (e.g., https://proofpoint.example.com/encryption/api/v1/users).
• No authentication required.

Exploitation Steps:

1. Identify the endpoint using Shodan or manual discovery.
2. Send a crafted HTTP POST request:

curl -X POST https://proofpoint.example.com/encryption/api/v1/users \
  -H "Content-Type: application/json" \
  -d '{"email": "attacker@controlled.com", "domain": "victim.com"}'

3. Verify account creation by attempting to send a spoofed email:

curl -X POST https://proofpoint.example.com/encryption/api/v1/send \
  -H "Content-Type: application/json" \
  -d '{"from": "ceo@victim.com", "to": "employee@victim.com", "subject": "Urgent", "body": "Send money"}'

Blue Team

Detection:

• Monitor for unusual POST requests to /encryption/api/v1/users from external IPs.
• Alert on creation of accounts with domains not matching the organization’s allowed list.
• Use the Sigma rule below to detect suspicious HTTP requests.

Mitigation:

• Block external access to the Proofpoint Encryption endpoint using a WAF or firewall.
• Implement authentication for all API endpoints.
• Apply input validation and rate limiting.

Indicators of Compromise (IOCs)

• Network IOCs:
  • POST requests to /encryption/api/v1/users with JSON payload containing email and domain fields.
  • Unusual email headers indicating spoofed sender addresses.
• Host IOCs:
  • New user accounts in Proofpoint Encryption logs with unexpected domains.
  • Log entries showing account creation without authentication.
• File IOCs:
  • None currently identified.

Detection Engineering

YARA Rule

rule CVE_2024_3676_Proofpoint_Account_Creation {
    meta:
        description = "Detects HTTP requests attempting to exploit CVE-2024-3676"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-3676"
    strings:
        $json_payload = /{"email":\s*"[^"]+",\s*"domain":\s*"[^"]+"}/
        $endpoint = "/encryption/api/v1/users"
    condition:
        $endpoint and $json_payload
}

Sigma Rule

title: Proofpoint Encryption Unauthorized Account Creation
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP POST requests to Proofpoint Encryption endpoint that may indicate exploitation of CVE-2024-3676
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/encryption/api/v1/users'
        cs-content-type: 'application/json'
    condition: selection
falsepositives:
    - Legitimate administrative account creation
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-3676 Proofpoint Encryption Account Creation Attempt"; flow:to_server; content:"POST"; http_method; content:"/encryption/api/v1/users"; http_uri; content:"application/json"; http_content_type; pcre:"/\"email\":\s*\"[^\"]+\",\s*\"domain\":\s*\"[^\"]+\"/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the vulnerable endpoint if not required, or restrict access to trusted IPs only.
2. Implement a Web Application Firewall (WAF) rule to block POST requests to /encryption/api/v1/users from untrusted sources.
3. Monitor logs for any unauthorized account creation attempts.

Long-Term Fix:

• Apply the vendor patch once released.
• Enforce authentication for all API endpoints.
• Conduct a security review of input validation and authorization logic.

Workarounds:

• Use network segmentation to isolate the Proofpoint Encryption service.
• Enable logging and alerting for all account creation events.

Valters IT
Securing Digital Frontiers