CVE-2020-37132: UltraVNC Launcher DoS Vulnerability

CVE-2020-37132 Overview

CVE-2020-37132 is a denial of service vulnerability affecting UltraVNC Launcher version 1.2.4.0. The vulnerability exists in the password configuration properties and allows local attackers to crash the application by providing an overly long input string. Specifically, attackers can paste a 300-character string into the password field, triggering an application crash and preventing normal launcher functionality.

Critical Impact

Local attackers can exploit this stack-based buffer overflow to crash UltraVNC Launcher, disrupting remote desktop connectivity and system administration workflows.

Affected Products

• UltraVNC Launcher 1.2.4.0

Discovery Timeline

• 2026-02-05 - CVE CVE-2020-37132 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2020-37132

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), which occurs when a program copies data to a fixed-length stack buffer without proper bounds checking. In the case of UltraVNC Launcher, the password input field does not enforce adequate length restrictions, allowing an attacker to submit input that exceeds the allocated buffer size.

When a user or attacker pastes an overly long string (approximately 300 characters) into the password configuration field, the application attempts to store this data in a stack-allocated buffer that cannot accommodate the input size. This results in stack memory corruption, causing the application to crash unexpectedly.

The attack requires local access to the system where UltraVNC Launcher is installed and some form of user interaction (accessing the password configuration dialog), which limits the attack surface compared to remotely exploitable vulnerabilities.

Root Cause

The root cause is improper input validation in the password handling routines of UltraVNC Launcher. The application fails to enforce proper length limits on user-supplied password input before copying it to a fixed-size stack buffer. This lack of boundary checking allows oversized input to overwrite adjacent stack memory, corrupting the execution state and triggering an unhandled exception.

Attack Vector

The attack vector is local, requiring the attacker to have access to the system where UltraVNC Launcher is installed. The exploitation scenario involves:

1. Opening UltraVNC Launcher and accessing the password configuration properties
2. Pasting an overly long string (300+ characters) into the password field
3. The application attempts to process the oversized input
4. The stack buffer overflow occurs, corrupting memory and causing the application to crash

This denial of service condition prevents legitimate users from configuring or using UltraVNC Launcher until the application is restarted. While this vulnerability does not directly enable code execution or data exfiltration, it can disrupt remote administration capabilities in environments relying on UltraVNC for remote access.

For detailed technical information, refer to the Exploit-DB #48290 entry and the Vulncheck Advisory for UltraVNC.

Detection Methods for CVE-2020-37132

Indicators of Compromise

• Unexpected crashes of uvnc_launcher.exe or related UltraVNC Launcher processes
• Application crash logs showing stack corruption or access violation exceptions in the password configuration module
• Multiple instances of UltraVNC Launcher crash events in Windows Event Logs within a short timeframe
• Unusual user activity patterns involving repeated access to the password configuration dialog

Detection Strategies

• Monitor endpoint process stability for UltraVNC Launcher (uvnc_launcher.exe) using endpoint detection and response (EDR) solutions
• Configure application crash monitoring to alert on repeated UltraVNC Launcher failures
• Implement file integrity monitoring on UltraVNC Launcher configuration files to detect unauthorized modifications
• Use SentinelOne's behavioral AI to detect anomalous application crashes that may indicate exploitation attempts

Monitoring Recommendations

• Enable Windows Error Reporting and centralize crash dump collection for analysis
• Deploy endpoint monitoring to track UltraVNC Launcher process health and restart patterns
• Implement logging for configuration changes to UltraVNC Launcher settings
• Review system logs regularly for patterns indicating repeated denial of service attacks against local applications

How to Mitigate CVE-2020-37132

Immediate Actions Required

• Inventory all systems running UltraVNC Launcher 1.2.4.0 and prioritize remediation
• Check the UVNC Official Site for updated versions that address this vulnerability
• Restrict local access to systems running vulnerable UltraVNC Launcher installations
• Consider implementing application whitelisting to prevent unauthorized modifications to UltraVNC Launcher configurations

Patch Information

Check the official UltraVNC website at https://www.uvnc.com/ for the latest version releases that may address this vulnerability. Review the Vulncheck Advisory for UltraVNC for additional remediation guidance and any available patches.

Workarounds

• Restrict access to UltraVNC Launcher configuration interfaces to trusted administrators only
• Implement least-privilege access controls to limit which users can modify UltraVNC Launcher settings
• Consider using alternative remote desktop solutions if a patched version is not available
• Deploy endpoint protection solutions like SentinelOne to monitor for and respond to application crashes indicative of exploitation