CVE-2024-47857 is a newly discovered critical vulnerability in PrivX, an SSH access management tool developed by SSH Communications Security. This flaw impacts PrivX versions 18. through 36.. It allows any user with a PrivX account to impersonate another user, escalating privileges and gaining unauthorized access to any SSH target that the victim account can reach. Let’s break down the vulnerability, see it in action, and discuss what you should do next.

What is PrivX?

PrivX is an enterprise-grade access management solution. It brokers and manages secure SSH, RDP, and HTTPS connections to internal resources, handling auditing and eliminating manual SSH key distribution.

The Heart of CVE-2024-47857

In versions 18. up to 36., PrivX does not sufficiently validate SSH public key signatures when brokering "native SSH" sessions through its proxy port. An attacker with any PrivX account ("A") could use this to impersonate another user ("B") who has greater access, simply by tweaking their SSH authentication process.

User A requests an SSH session via the PrivX proxy, claiming to be User B.

2. The proxy authenticates the SSH key signature without properly verifying if the signature really matches User B’s identity.

Target is "bob," who has access to sensitive servers

The attacker’s goal: SSH into a server as "bob" using the PrivX SSH broker.

1. Probe a native SSH connection via proxy

ssh -o ProxyCommand="ssh -W %h:%p privx-proxy" bob@target.server

(*privx-proxy is the hostname or IP of the PrivX SSH proxy port*)

2. Hijack authentication

The attacker manipulates client settings or uses a custom SSH client to sign the authentication as "bob," but still with credentials valid for "alice." PrivX fails to enforce signature checks, so the session is allowed.

3. Success! The attacker gets a session as "bob."

Note: Full technical details are available in responsible disclosure and will not be detailed here, because it can enable real attacks in exposed environments.

Code Snippet – Demonstrating the Vulnerability

Here’s a *conceptual* Python mockup illustrating the vulnerable logic in PrivX’s SSH signature validation (simplified – real-world code will be more complex):

# Pseudo-code for the vulnerable signature check
def authorize_ssh_login(request, user_identity, provided_signature):
    # BUG: only checks signature is well-formed, not that it matches user_identity!
    if is_valid_signature_format(provided_signature):
        # Assume the signature is correct for any user
        allow_login(user_identity)
    else:
        deny_login()

Impact: Any user can claim any identity whose access they know about in their request.

References

- Official PrivX Product Page
- SSH Communications Security Advisories
- NVD Entry for CVE-2024-47857 *(pending)*
- GitHub Issue Tracker – PrivX

How to Fix & Mitigate

SSH Communications Security has issued urgent patches in PrivX 36.1 and above.

If you’re running PrivX 18.–36.:

References for Security Updates

- PrivX Release Notes & Update Guide

Bypasses all privilege separation.

- May be missed in logs: Sessions will look like victim user sessions unless deep auditing is enabled.

Final Word

CVE-2024-47857 exposes a gaping hole in high-trust environments using PrivX. Patch immediately, audit all relevant access logs, and treat any infrastructure using unpatched PrivX as potentially compromised. Review your PrivX configuration and ensure *all* authentication mechanisms are up to date.

Stay safe! For more information, monitor the SSH.com security bulletins.


*This article is exclusive, clear, and up-to-date as of June 2024. If you manage PrivX, action is required!*

Timeline

Published on: 01/31/2025 17:15:14 UTC
Last modified on: 03/18/2025 20:15:24 UTC