CVE-2019-25570: RealTerm Serial Terminal DoS Vulnerability

CVE-2019-25570 Overview

CVE-2019-25570 is a denial of service vulnerability affecting RealTerm Serial Terminal version 2.0.0.70. The vulnerability allows local attackers to crash the application by supplying an excessively long string in the Port field. Specifically, an attacker can paste a buffer of 1000 characters into the Port input field and click the open button to trigger an application crash.

Critical Impact

Local attackers can cause application instability and denial of service by exploiting improper input handling in the Port field, potentially disrupting serial communication workflows and industrial control system operations.

Affected Products

• RealTerm Serial Terminal 2.0.0.70
• Crun RealTerm

Discovery Timeline

• 2026-03-21 - CVE-2019-25570 published to NVD
• 2026-03-24 - Last updated in NVD database

Technical Details for CVE-2019-25570

Vulnerability Analysis

This vulnerability is classified under CWE-1260 (Improper Handling of Physical or Environmental Conditions). The RealTerm Serial Terminal application fails to properly validate and sanitize user input in the Port configuration field before processing. When a user enters an excessively long string (approximately 1000 characters or more) into the Port field and attempts to open the connection, the application experiences a buffer-related crash.

The attack requires local access and user interaction to trigger. An attacker must either have direct access to the system running RealTerm or convince a user to paste malicious input into the Port field. While this limits the attack surface, it remains a concern in environments where RealTerm is used for serial communications in industrial control systems, embedded development, or laboratory equipment management.

Root Cause

The root cause of this vulnerability stems from insufficient input validation in the Port field handler. The application does not enforce proper length restrictions on user-supplied input before allocating memory or processing the string. When an oversized string is submitted, it exceeds the expected buffer boundaries, causing the application to crash.

Attack Vector

The attack vector is local and requires user interaction. The exploitation process involves:

1. An attacker prepares a malicious string containing approximately 1000 or more characters
2. The attacker pastes this string into the Port input field within the RealTerm application
3. Upon clicking the "Open" button to establish a serial connection, the application crashes

The vulnerability cannot be exploited remotely without first gaining local access to the target system. For detailed technical analysis, refer to the Exploit-DB #46390 entry and the VulnCheck Denial of Service Advisory.

Detection Methods for CVE-2019-25570

Indicators of Compromise

• Unexpected RealTerm application crashes or terminations
• Windows Application Event Log entries showing RealTerm crash events
• Presence of unusually long strings in configuration files or clipboard history
• Multiple rapid restart attempts of the RealTerm application

Detection Strategies

• Monitor for RealTerm process crashes using endpoint detection and response (EDR) tools
• Implement application crash monitoring on systems where RealTerm is deployed
• Enable Windows Error Reporting to capture crash dumps for forensic analysis
• Use SentinelOne Singularity platform to detect anomalous application behavior patterns

Monitoring Recommendations

• Configure alerts for repeated application crashes on critical industrial control workstations
• Monitor clipboard activity for suspiciously long strings being copied on systems running RealTerm
• Implement application whitelisting policies to track unauthorized modifications to RealTerm installations
• Review system logs periodically for patterns indicating exploitation attempts

How to Mitigate CVE-2019-25570

Immediate Actions Required

• Restrict access to systems running RealTerm Serial Terminal to authorized personnel only
• Implement least-privilege access controls on workstations where RealTerm is installed
• Educate users about the risks of pasting untrusted content into application input fields
• Consider replacing RealTerm with alternative serial terminal software if a patched version is unavailable

Patch Information

At the time of this analysis, no official vendor patch has been identified in the available CVE data. Users should monitor the RealTerm SourceForge project and the RealTerm file downloads page for potential updates. Organizations using RealTerm in production environments should evaluate alternative serial terminal applications with better input validation controls.

Workarounds

• Limit physical access to workstations running RealTerm to trusted users
• Implement application sandboxing using Windows Sandbox or containerization technologies
• Configure clipboard restrictions through group policy to prevent large clipboard content on sensitive systems
• Use SentinelOne to monitor and protect endpoints running vulnerable RealTerm installations

# Configuration example: Restrict RealTerm execution using Windows AppLocker
# Note: Apply through Group Policy or local security policy

# Create AppLocker rule to restrict RealTerm to specific users
# Path: Computer Configuration > Windows Settings > Security Settings > Application Control Policies > AppLocker

# Example PowerShell to check for RealTerm installations
Get-WmiObject -Class Win32_Product | Where-Object { $_.Name -like "*RealTerm*" }

# Monitor for crash events in Windows Event Log
Get-WinEvent -FilterHashtable @{LogName='Application'; ProviderName='Application Error'} | 
    Where-Object { $_.Message -like "*realterm*" } | Select-Object TimeCreated, Message