Executive Summary

CVE-2020-37128 is a vulnerability in ZOC Terminal version 7.25.5 that involves a script processing flaw. Specifically, it allows local attackers to crash the application by loading a maliciously crafted REXX script file. The attack works by creating an oversized script containing about 20,000 repeated characters, which triggers a stack-based buffer overflow and causes the application to crash.

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Impact Analysis

This vulnerability can impact you by causing a denial of service (DoS) condition on the affected system. An attacker with local access can crash the ZOC Terminal application by loading a specially crafted REXX script, disrupting your ability to use the terminal emulator for secure server access and related tasks.

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Compliance Impact

I don't know

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Detection Guidance

This vulnerability is local and triggered by loading a maliciously crafted REXX script file containing an oversized script with approximately 20,000 repeated characters. Detection involves identifying if such a crafted REXX script file has been loaded or executed in ZOC Terminal version 7.25.5.

To detect exploitation attempts, monitor for unusual script execution activity within ZOC Terminal, especially scripts with abnormally large payloads or repeated characters.

A practical approach is to check for the presence of suspicious REXX script files (e.g., files with .zrx extension) containing large repeated characters. For example, on Windows, you can use PowerShell to search for large .zrx files:

• Get-ChildItem -Path C:\path\to\scripts -Filter *.zrx | Where-Object { $_.Length -gt 100000 }

Additionally, if you have access to logs or can monitor the ZOC Terminal interface, look for script start events with unusually large scripts.

Since the exploit involves loading a script via the ZOC Terminal interface (Script > Start REXX Script), monitoring user actions or scripting activity in the application may help detect attempts.

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Mitigation Strategies

To mitigate this vulnerability, immediate steps include:

• Avoid loading or executing untrusted or suspicious REXX script files, especially those with unusually large or repetitive content.
• Restrict local user access to the ZOC Terminal application to trusted users only, as the vulnerability requires local access.
• If possible, upgrade ZOC Terminal to a version later than 7.25.5 where this vulnerability is fixed or apply any patches provided by the vendor.
• Implement monitoring to detect attempts to load large or malformed REXX scripts.
• Educate users about the risk of running unverified scripts within ZOC Terminal.

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