TL;DR:
A recently discovered security bug—CVE-2024-5921—in Palo Alto Networks’ GlobalProtect app makes it possible for attackers to connect the VPN client to rogue servers by exploiting weak certificate validation. Attackers may be able to install malicious certificates and subsequently deploy malware signed with those certs. Here’s what you need to know, including technical details, code snippets, and how you can protect yourself.

What is GlobalProtect and Why This Is a Big Deal

GlobalProtect is a very widely used VPN client for connecting enterprise endpoints securely to internal resources. If a VPN client can be tricked into accepting fake servers, the consequences can range from malware infection to network compromise.

CVE-2024-5921 is an insufficient certificate validation issue: The GlobalProtect client can be coaxed into connecting to a server pretending to be the real one, but is actually under attacker control. All an attacker needs is to be on the same local network or have local, non-admin access.

Attack setup:

An attacker either gains access as a low-privileged user on the target device, or is able to join the victim's subnet (wifi or ethernet LAN at an office, airport, etc).

Certificate attack:

The attacker injects or offers a malicious root CA certificate on the victim’s device. Since GlobalProtect does not strictly require server certificate validation, the app accepts the malicious server.

Malware deployment:

With the fake certificate trusted, attackers can deliver malware signed with it, making it appear legitimate to the system and sometimes bypassing endpoint security.

Technical Details – Behind the Scenes

The underlying vulnerability arises because the GlobalProtect client does not fully or correctly check the authenticity of the VPN gateway’s certificate chain during the connection process.

Here’s a simplified pseudocode example of what *should* happen

def validate_server_certificate(cert, trusted_CAs):
    # Best practice: validate the full chain, hostname, validity period, and revocation status
    if not cert.issued_by in trusted_CAs:
        return False
    if not cert.is_valid():
        return False
    if not cert.subject_matches_hostname():
        return False
    if cert.is_revoked():
        return False
    return True

# Bad, insufficient validation (simplified for illustration):
def broken_certificate_validation(cert, trusted_CAs):
    # Only checks if the certificate *exists*, not if it's trusted or matches anything
    if cert:
        return True
    return False

In this case, GlobalProtect’s logic is closer to the second function, allowing any presented certificate—even those from newly injected, attacker-controlled roots—to be accepted.

Real-World Exploit Scenario

Suppose Alice, a corporate user, connects her laptop to an open airport Wi-Fi. Mallory, sitting nearby, sets up a fake GlobalProtect server and broadcasts it.

Now, Mallory can push fake software updates or intercept and modify traffic.

4. Alice’s machine accepts these updates as legitimate, since they’re signed by the now "trusted" (but actually malicious) CA.

PoC: How an Attacker Might Inject a Malicious Certificate (For Educational Purposes Only!)

*To be clear: Don’t use this against networks you don’t own! This is purely to illustrate the danger.*

Python Demo: (Requires admin privileges)

import subprocess

def install_malicious_cert(cert_path):
    command = [
        'certutil',   # Windows built-in certificate management
        '-addstore',
        'Root',
        cert_path
    ]
    subprocess.run(command)

# Path to attacker's crafted root CA cert
install_malicious_cert('malicious_rootCA.cer')

Once this is done, any software the attacker signs with this certificate will look "trusted" unless strict validation is implemented by each app.

Update GlobalProtect to the latest version immediately.

See the official advisory for patch details.

Monitor for unrecognized root CAs and signed binaries on endpoints.

- Educate end-users: Warn them not to connect to public Wi-Fi with VPN clients that aren’t up to date.

References & Further Reading

- 🚨 Palo Alto Networks original advisory
- 📝 Subscribe to Palo Alto’s RSS feed for future security advisories
- 👨‍💻 General guide to certificate authentication
- 🦠 How certificate injection attacks work

Closing Thoughts

CVE-2024-5921 is a textbook example of why proper certificate validation is essential—especially on trusted endpoints. If your company uses Palo Alto’s GlobalProtect, make patching a top priority and review your device certificate policies. One weak spot can be all it takes for malware to slip through the gates.

→ Don’t forget to subscribe to Palo Alto Networks’ RSS feed for the latest on this and other advisories.

Timeline

Published on: 11/27/2024 04:15:14 UTC
Last modified on: 02/20/2025 23:15:11 UTC