CVE-2020-37128: ZOC Terminal 7.25.5 DoS Vulnerability

CVE-2020-37128 Overview

CVE-2020-37128 is a stack-based buffer overflow vulnerability affecting ZOC Terminal version 7.25.5. The vulnerability exists in the application's REXX script processing functionality, which fails to properly validate the size of input data when loading script files. Local attackers can exploit this flaw by crafting a malicious REXX script file containing approximately 20,000 repeated characters, causing the application to crash and resulting in a denial of service condition.

Critical Impact
Successful exploitation allows local attackers to crash ZOC Terminal through maliciously crafted REXX script files, disrupting terminal emulation services and potentially affecting critical administrative workflows that depend on the application.

Affected Products

ZOC Terminal version 7.25.5
Emtec ZOC Terminal (Windows and macOS versions)

Discovery Timeline

2026-02-05 - CVE-2020-37128 published to NVD
2026-02-05 - Last updated in NVD database

Technical Details for CVE-2020-37128

Vulnerability Analysis

The vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), which occurs when a program writes data beyond the boundaries of a pre-allocated stack buffer. In the case of ZOC Terminal 7.25.5, the script processing engine does not adequately check the length of input data when parsing REXX script files.

When a user opens or executes a REXX script through ZOC Terminal, the application reads the script content into a stack-allocated buffer. The absence of proper bounds checking allows an attacker to provide input that exceeds the buffer's capacity, overwriting adjacent memory on the stack. While this specific vulnerability results in application termination (denial of service), stack-based buffer overflows can potentially be leveraged for code execution in certain circumstances.

The attack requires local access and user interaction—specifically, the victim must load the malicious script file into the application.

Root Cause

The root cause of CVE-2020-37128 is insufficient input validation in ZOC Terminal's REXX script parser. The application allocates a fixed-size buffer on the stack to process script content but does not verify that incoming data fits within these boundaries. When processing a script containing approximately 20,000 repeated characters, the buffer overflows, corrupting stack memory and causing the application to crash.

Attack Vector

The attack vector is local, requiring the attacker to either:

Have direct access to the target system to place a malicious REXX script file
Convince a user to download and open a malicious script file through social engineering

The exploitation is straightforward—an attacker generates an oversized REXX script file with repeated characters (approximately 20,000 bytes of padding) and delivers it to the victim. When the victim opens this script in ZOC Terminal, the application crashes due to the stack buffer overflow.

Technical details about the exploitation mechanism can be found in the Exploit-DB #48302 entry and the VulnCheck Security Advisory.

Detection Methods for CVE-2020-37128

Indicators of Compromise

Presence of unusually large REXX script files (.rexx, .rex) in user directories or download locations
ZOC Terminal crash logs or Windows Error Reporting events indicating application termination
Unexpected ZOC Terminal process terminations without user-initiated closure
Script files containing repetitive character patterns or suspicious padding

Detection Strategies

Monitor for ZOC Terminal crash events in Windows Event Logs (Application log, event ID 1000 for application crashes)
Implement file integrity monitoring for directories containing REXX scripts used by ZOC Terminal
Deploy endpoint detection rules to identify unusually large script files being opened by zoc.exe
Use SentinelOne's behavioral AI to detect anomalous process terminations and potential exploitation attempts

Monitoring Recommendations

Enable application crash logging and forward crash reports to centralized logging infrastructure
Monitor for repeated ZOC Terminal crashes that may indicate exploitation attempts
Track file system activity for creation of REXX script files exceeding normal size thresholds
Implement user awareness training regarding suspicious script files received via email or download

How to Mitigate CVE-2020-37128

Immediate Actions Required

Upgrade ZOC Terminal to the latest available version from Emtec
Restrict execution of REXX scripts to trusted, validated sources only
Implement application whitelisting to control which scripts can be loaded into ZOC Terminal
Educate users about the risks of opening script files from untrusted sources

Patch Information

Users should check the Emtec website for the latest version of ZOC Terminal that addresses this vulnerability. The vendor advisory and patch information should be reviewed for specific remediation guidance. Additional technical details are available in the VulnCheck Security Advisory.

Workarounds

Disable or restrict REXX script functionality if not required for operational needs
Implement file size validation for script files before opening them in ZOC Terminal
Use file filtering solutions to block oversized script files from reaching end users
Deploy endpoint protection solutions like SentinelOne to detect and prevent exploitation attempts

bash

# Example: Block large REXX files using Windows PowerShell
# Monitor and alert on REXX files larger than 10KB in user directories
Get-ChildItem -Path "$env:USERPROFILE" -Recurse -Include *.rexx,*.rex | 
Where-Object { $_.Length -gt 10KB } | 
ForEach-Object { Write-Warning "Suspicious script file detected: $($_.FullName)" }