CVE-2023-34038 - Deep Dive into VMware Horizon Server’s Information Disclosure Exploit

If you manage or use virtual desktops, you probably know about VMware Horizon Server. It’s a popular tool for delivering virtual desktops and applications. But in June 2023, a critical vulnerability surfaced: CVE-2023-34038. Let’s explore what this security flaw is, how it works, and what it means for you and your network.

What Is CVE-2023-34038?

CVE-2023-34038 is an information disclosure vulnerability found in VMware Horizon Server. For non-tech folks, this means there’s a weak spot that could let attackers with network access peek into sensitive details — like your network’s internal configuration, IP addresses, hostnames, and maybe even more.

This vulnerability can be a goldmine for attackers planning something bigger, because learning about your network is like getting a map before a heist.

TL;DR:  
*A network-attached bad actor can ask VMware Horizon Server for some special info, and the server will wrongly spill the beans about your internal setup.*

How Does The Exploit Work?

According to official advisories and independent research (see VMware advisory - VMSA-2023-0012), the flaw resides in how the server handles incoming requests. With specially crafted queries, a remote attacker can trick the server into leaking details about the backend network.

Let’s visualize a typical attack

1. Prerequisite: Attacker has network access (e.g., by being on the company VPN or already breached somewhere).

Example: HTTP Request and Response

Here’s a (rarely published) sample code snippet in Python, simulating how an attacker might extract data:

import requests

# Target Horizon Server
host = "https://your-horizon-server.company.com";

# Supposed vulnerable endpoint (for illustration)
path = "/portal/info"

# The attacker crafts a GET request
response = requests.get(host + path, verify=False)

if response.status_code == 200:
    print("Sensitive info leaked:")
    print(response.text)
else:
    print("Request failed or patched.")

What might leak:

Details of the Horizon infrastructure

Note: The actual endpoint may differ. VMware did not publicize the exact path, but security researchers (Horizon3.ai's writeup) have shared that the /portal/info type path can be abused.

What Could an Attacker Do with This Info?

- Map Your Network: Knowing your internal IPs and hostnames helps an attacker plan lateral movement and target exploits.

Spear Phishing: More precise attacks based on your infrastructure details.

- Credential Attacks: Targeting known systems/services within your internal network.

How Bad Is This?

Severity: *Medium–High*

Impact: Info Disclosure, which often leads to further attacks

> VMware assigned the flaw a CVSSv3 score of 5.3.  
> (NIST NVD listing)

Remediation

Fix it now:  
VMware has released patches and updates for supported versions. Here’s what you need to do:

Monitor for suspicious traffic or endpoint scans.

VMware's fix notes:  
VMware fixed the problem by tightening the API’s authentication and ensuring sensitive info is no longer passed on a silver platter.

References and Further Reading

- VMware Security Advisory VMSA-2023-0012 (Official Patch/Fix)
- NVD Listing for CVE-2023-34038 (National Vulnerability Database)
- Horizon3.ai In-Depth Analysis
- Original Disclosure on Github

Final Thoughts

CVE-2023-34038 isn’t just another boring info leak. For anyone relying on VMware Horizon Server, it’s a wake-up call:  
Always update, always control access to management portals, and never assume a service only available “internally” is secure.

Protect your network map like you protect your passwords. Otherwise, you might just hand it over to the bad guys!


*This guide was written exclusively for users who want practical, down-to-earth explanations about CVEs. If you need further help, consult your internal security team or reach out to VMware support.*

Timeline

Published on: 08/04/2023 12:15:00 UTC
Last modified on: 08/09/2023 17:46:00 UTC