CVE-2020-37164: AbsoluteTelnet DoS Vulnerability

CVE-2020-37164 Overview

CVE-2020-37164 is a denial of service vulnerability affecting AbsoluteTelnet version 11.12. The vulnerability allows local attackers to crash the application by supplying an oversized license name. Attackers can generate a 2500-character payload and paste it into the license entry field to trigger an application crash, resulting in denial of service conditions.

Critical Impact

Local attackers can crash AbsoluteTelnet by supplying an oversized license name string exceeding expected buffer limits, causing application instability and denial of service.

Affected Products

• AbsoluteTelnet 11.12
• Celestial Software AbsoluteTelnet products with vulnerable license entry handling

Discovery Timeline

• 2026-02-07 - CVE-2020-37164 published to NVD
• 2026-02-09 - Last updated in NVD database

Technical Details for CVE-2020-37164

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The vulnerability exists in the license entry field of AbsoluteTelnet 11.12, where the application fails to properly validate the length of user-supplied input before processing it.

When a user enters a license name into the application's registration dialog, the input is copied into a fixed-size buffer without adequate bounds checking. By supplying a string of approximately 2500 characters or more, an attacker can overflow this buffer, corrupting adjacent memory and causing the application to crash.

The local attack vector requires user interaction, as the attacker must either have direct access to the application interface or convince a legitimate user to paste the malicious payload into the license field. While this limits the attack surface compared to remote vulnerabilities, it still presents a risk in shared computing environments or through social engineering attacks.

Root Cause

The root cause is improper input validation in the license name handling routine. The application allocates a fixed-size buffer for storing license information but does not enforce length restrictions on user input before copying data into this buffer. This classic buffer overflow pattern (CWE-120) occurs when strcpy() or similar unbounded copy functions are used without first verifying that the source data fits within the destination buffer.

Attack Vector

The attack is executed locally through the following method:

1. The attacker launches AbsoluteTelnet 11.12 on a target system
2. The attacker navigates to the license registration dialog
3. A payload string of approximately 2500+ characters is generated
4. The payload is pasted into the license name entry field
5. Upon processing the input, the application crashes due to buffer overflow

The vulnerability requires local access and user interaction to exploit. An attacker could potentially leverage this in scenarios where they have limited access to a shared system or through social engineering tactics that convince users to enter malicious license strings.

For technical exploitation details, refer to the Exploit-DB #48005 entry and the VulnCheck Advisory on AbsoluteTelnet.

Detection Methods for CVE-2020-37164

Indicators of Compromise

• Unexpected AbsoluteTelnet application crashes or termination events
• Windows Event Log entries indicating application faults in AbsoluteTelnet.exe
• Presence of crash dump files related to AbsoluteTelnet processes
• User reports of application instability when entering license information

Detection Strategies

• Monitor for abnormal process termination events associated with AbsoluteTelnet
• Implement application-level logging to capture crashes and error conditions
• Deploy endpoint detection solutions capable of identifying buffer overflow attempts
• SentinelOne Singularity Platform can detect anomalous application behavior and memory corruption attempts

Monitoring Recommendations

• Enable Windows Error Reporting to capture crash telemetry for AbsoluteTelnet
• Configure endpoint protection to alert on repeated application crashes
• Review system event logs for patterns indicating exploitation attempts
• Monitor for social engineering attempts that may deliver malicious license strings

How to Mitigate CVE-2020-37164

Immediate Actions Required

• Update AbsoluteTelnet to the latest available version from Celestial Software
• Restrict access to the AbsoluteTelnet installation on shared systems
• Educate users about the risks of entering untrusted data into license fields
• Deploy endpoint protection solutions to detect and prevent exploitation

Patch Information

Organizations should check Celestial Software Homepage for the latest security updates and patches addressing this vulnerability. It is recommended to upgrade to a version newer than 11.12 that includes proper input validation for the license entry field.

Workarounds

• Limit access to AbsoluteTelnet to trusted users only on multi-user systems
• Implement application whitelisting policies to control who can execute the application
• Monitor for and block attempts to paste excessively long strings into application dialogs
• Consider using alternative terminal emulation software until a patch is applied
• Deploy SentinelOne endpoint protection to detect and prevent buffer overflow exploitation attempts