CVE-2023-34038: VMware Horizon Information Disclosure

CVE-2023-34038 Overview

VMware Horizon Server contains an information disclosure vulnerability that allows a malicious actor with network access to potentially access information relating to the internal network configuration. This vulnerability affects multiple versions of VMware Horizon Client, enabling unauthorized exposure of sensitive infrastructure details without requiring authentication.

Critical Impact

Attackers with network access can retrieve internal network configuration information, potentially enabling reconnaissance for further attacks against the organization's infrastructure.

Affected Products

• VMware Horizon Client 2006
• VMware Horizon Client 2012
• VMware Horizon Client 2103
• VMware Horizon Client 2106
• VMware Horizon Client 2111
• VMware Horizon Client 2111.1
• VMware Horizon Client 2203
• VMware Horizon Client 2212

Discovery Timeline

• 2023-08-04 - CVE-2023-34038 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-34038

Vulnerability Analysis

This information disclosure vulnerability in VMware Horizon Server exposes internal network configuration details to unauthorized actors with network access. The vulnerability enables attackers to gather reconnaissance information about the target environment without requiring any privileges or user interaction. The attack can be executed remotely over the network with low complexity, making it accessible to a wide range of threat actors.

While the vulnerability is limited to read-only access of configuration information (no impact on integrity or availability), the disclosed network configuration data could be leveraged as part of a multi-stage attack to map internal infrastructure, identify additional targets, or craft more sophisticated exploits against the organization's systems.

Root Cause

The vulnerability stems from improper access controls or insufficient validation when handling requests that expose internal network configuration data. VMware Horizon Server fails to adequately protect sensitive configuration information from being accessed by unauthenticated or unauthorized network actors.

Attack Vector

The attack vector is network-based, requiring an attacker to have network connectivity to the vulnerable VMware Horizon Server instance. The exploitation requires:

1. Network access to the target VMware Horizon Server
2. No authentication credentials required
3. No user interaction needed
4. Direct query or request to the vulnerable endpoint

The attacker can craft specific requests to the Horizon Server that result in the disclosure of internal network configuration details. This information could include network topology data, internal IP addressing schemes, or other configuration parameters that should remain confidential.

Detection Methods for CVE-2023-34038

Indicators of Compromise

• Unusual or unexpected network reconnaissance traffic directed at VMware Horizon Server instances
• Anomalous queries or requests attempting to extract configuration information from Horizon Server endpoints
• Log entries showing unauthenticated access attempts to configuration-related resources
• Network traffic patterns indicating systematic probing of Horizon Server services

Detection Strategies

• Monitor VMware Horizon Server logs for unusual access patterns or queries targeting configuration endpoints
• Implement network intrusion detection rules to identify potential information disclosure attempts
• Deploy SentinelOne Singularity Platform to detect and alert on suspicious activity targeting virtualization infrastructure
• Enable detailed audit logging on VMware Horizon components to capture potential exploitation attempts

Monitoring Recommendations

• Configure SIEM rules to alert on anomalous access patterns to VMware Horizon Server infrastructure
• Establish baseline network behavior for Horizon Server communications and alert on deviations
• Monitor for sequential reconnaissance activities that may indicate an attacker leveraging disclosed information
• Review VMware Horizon Server access logs regularly for signs of unauthorized information gathering

How to Mitigate CVE-2023-34038

Immediate Actions Required

• Review the VMware Security Advisory VMSA-2023-0017 for detailed remediation guidance
• Identify all VMware Horizon Client installations running affected versions (2006 through 2212)
• Prioritize patching internet-facing or externally accessible Horizon Server instances
• Implement network segmentation to limit exposure of Horizon Server infrastructure

Patch Information

VMware has released security updates to address this vulnerability. Administrators should consult the VMware Security Advisory VMSA-2023-0017 for specific patch versions and update instructions. Organizations should upgrade VMware Horizon Client to the latest patched version as recommended by VMware.

Workarounds

• Restrict network access to VMware Horizon Server to only authorized users and systems using firewall rules
• Implement additional network segmentation to isolate Horizon infrastructure from untrusted networks
• Enable enhanced logging and monitoring on all Horizon Server components pending patch deployment
• Consider deploying a Web Application Firewall (WAF) or reverse proxy to filter malicious requests

# Example: Restrict network access to VMware Horizon Server using iptables
# Allow only specific trusted network ranges to access Horizon Server
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP

# Enable detailed logging for monitoring purposes
iptables -A INPUT -p tcp --dport 443 -j LOG --log-prefix "Horizon-Access: "