CVE-2020-37165: AbsoluteTelnet DoS Vulnerability

CVE-2020-37165 Overview

CVE-2020-37165 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. Specifically, attackers can generate a 2500-character payload and paste it into the license name field to trigger an application crash. This is classified as a buffer overflow vulnerability (CWE-120: Buffer Copy without Checking Size of Input).

Critical Impact

Local attackers can cause a denial of service condition by crashing AbsoluteTelnet through the license name input field, disrupting terminal and SSH operations for affected users.

Affected Products

• AbsoluteTelnet 11.12
• Celestial Software AbsoluteTelnet (prior versions may also be affected)

Discovery Timeline

• 2026-02-07 - CVE CVE-2020-37165 published to NVD
• 2026-02-09 - Last updated in NVD database

Technical Details for CVE-2020-37165

Vulnerability Analysis

This vulnerability stems from a classic buffer overflow condition (CWE-120) in the license name handling functionality of AbsoluteTelnet 11.12. The application fails to properly validate the length of user input when processing the license name field, allowing an attacker to provide an input that exceeds the allocated buffer size. When a payload of approximately 2500 characters is supplied, the application crashes due to memory corruption.

The attack requires local access and some user interaction to exploit, as the attacker must either directly access the application or convince a user to paste the malicious payload into the license name field. While this limits the attack surface compared to remotely exploitable vulnerabilities, it still presents a risk in multi-user environments or scenarios where social engineering is employed.

Root Cause

The root cause is improper input validation in the license name processing routine. The application allocates a fixed-size buffer for the license name but does not enforce input length restrictions before copying user-supplied data into this buffer. This allows data to overflow beyond the buffer boundaries, corrupting adjacent memory and causing the application to crash.

This is a textbook example of CWE-120 (Buffer Copy without Checking Size of Input), where the developer failed to implement bounds checking before performing a memory copy operation.

Attack Vector

The attack vector is local, requiring the attacker to have access to the target system where AbsoluteTelnet is installed. The exploitation process involves:

1. Generating a payload string of approximately 2500 characters
2. Opening AbsoluteTelnet 11.12 on the target system
3. Navigating to the license name input field
4. Pasting or entering the oversized payload string
5. The application crashes when attempting to process the oversized input

The vulnerability does not require elevated privileges to exploit, but does require user interaction to trigger the vulnerable code path. Additional technical details are available in the Exploit-DB #48006 advisory.

Detection Methods for CVE-2020-37165

Indicators of Compromise

• Unexpected AbsoluteTelnet application crashes or termination events
• Windows Error Reporting (WER) crash dumps referencing AbsoluteTelnet with memory access violations
• Abnormally large license name values in application configuration files or registry entries
• User reports of application instability when accessing license settings

Detection Strategies

• Monitor for repeated application crash events associated with AbsoluteTelnet.exe in Windows Event Logs
• Implement application whitelisting and integrity monitoring to detect unauthorized modifications
• Configure endpoint detection rules to identify buffer overflow patterns in process memory
• Review Windows Application Event Log for Application Error events (Event ID 1000) related to AbsoluteTelnet

Monitoring Recommendations

• Enable application crash dump collection for forensic analysis of potential exploitation attempts
• Configure SIEM rules to correlate AbsoluteTelnet crash events with suspicious user activity
• Monitor registry keys and configuration files associated with AbsoluteTelnet license information for anomalous changes

How to Mitigate CVE-2020-37165

Immediate Actions Required

• Check the Celestial Software Homepage for updated versions of AbsoluteTelnet that address this vulnerability
• Restrict local access to systems running vulnerable versions of AbsoluteTelnet to trusted users only
• Consider using alternative terminal/SSH client software until a patch is available
• Implement application control policies to limit which users can modify AbsoluteTelnet settings

Patch Information

No official patch information is available in the CVE data at this time. Users are advised to check with Celestial Software directly for updated versions of AbsoluteTelnet. Additional advisory information is available from VulnCheck Advisory - AbsoluteTelnet DoS.

Workarounds

• Restrict user access to AbsoluteTelnet license configuration options where possible
• Implement endpoint protection solutions that can detect and prevent buffer overflow exploitation attempts
• Consider deploying application sandboxing to contain potential crashes and prevent system-wide impact
• Train users to avoid pasting untrusted content into application configuration fields