CVE-2020-37166: AbsoluteTelnet DoS Vulnerability

CVE-2020-37166 Overview

CVE-2020-37166 is a buffer overflow vulnerability affecting AbsoluteTelnet version 11.12. The vulnerability exists in the SSH2 username input field and allows local attackers to crash the application by overwriting the username field with a 1000-byte buffer. This results in a denial of service condition where the application becomes unresponsive and terminates.

Critical Impact

Local attackers can cause a complete denial of service by exploiting the buffer overflow in the SSH2 username field, rendering the AbsoluteTelnet application unusable.

Affected Products

• AbsoluteTelnet 11.12
• Celestial Software AbsoluteTelnet (SSH2 client functionality)

Discovery Timeline

• 2026-02-07 - CVE-2020-37166 published to NVD
• 2026-02-09 - Last updated in NVD database

Technical Details for CVE-2020-37166

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The application fails to properly validate the length of user-supplied input in the SSH2 username field before copying it into a fixed-size buffer. When an attacker supplies a specially crafted input exceeding the expected buffer size (approximately 1000 bytes), the application experiences memory corruption that leads to application instability and termination.

The local attack vector means that exploitation requires the attacker to have local access to the system where AbsoluteTelnet is installed. While this limits the attack surface compared to remote vulnerabilities, it remains a concern in shared computing environments or scenarios where malicious insiders may be present.

Root Cause

The root cause of this vulnerability is improper input validation in the SSH2 username handling code. The application does not enforce adequate boundary checks when processing username input, allowing excessively long strings to overflow the allocated buffer space. This is a fundamental secure coding issue where input length validation should occur before any buffer copy operations.

Attack Vector

The attack requires local access to the target system running AbsoluteTelnet 11.12. An attacker can trigger the vulnerability by:

1. Accessing the AbsoluteTelnet application on the local system
2. Navigating to the SSH2 connection configuration
3. Inputting a specially crafted 1000-byte string in the username field
4. Triggering the application to process the oversized input

The resulting buffer overflow corrupts adjacent memory structures, causing the application to crash or become unresponsive. This is a denial of service attack that disrupts the availability of the SSH client functionality.

For technical details on the exploitation mechanism, refer to the Exploit-DB #48010 entry and the VulnCheck Advisory.

Detection Methods for CVE-2020-37166

Indicators of Compromise

• Unexpected crashes or termination of the AbsoluteTelnet application
• Application logs showing abnormally long username entries in SSH2 connection attempts
• Windows Event Logs indicating application fault with AbsoluteTelnet process
• Core dumps or crash reports associated with the AbsoluteTelnet executable

Detection Strategies

• Monitor for repeated AbsoluteTelnet application crashes on endpoints
• Implement endpoint detection rules for process termination anomalies affecting AbsoluteTelnet.exe
• Review application configuration files for suspicious or abnormally long username values
• Deploy SentinelOne Singularity to detect and alert on exploitation attempts targeting buffer overflow conditions

Monitoring Recommendations

• Enable application crash monitoring on systems running AbsoluteTelnet
• Configure alerts for multiple application restarts within a short timeframe
• Review system stability logs for patterns consistent with denial of service attacks
• Implement user activity monitoring to detect potential insider threats attempting exploitation

How to Mitigate CVE-2020-37166

Immediate Actions Required

• Upgrade AbsoluteTelnet to the latest available version from Celestial Software
• Restrict local access to systems running AbsoluteTelnet to trusted users only
• Implement application whitelisting to prevent unauthorized modifications to the AbsoluteTelnet installation
• Consider deploying alternative SSH clients if patching is not immediately feasible

Patch Information

Users should check the Celestial Software Homepage for the latest version of AbsoluteTelnet that addresses this vulnerability. Ensure all instances of AbsoluteTelnet 11.12 are identified across the environment and scheduled for upgrade.

Workarounds

• Limit user access to systems with AbsoluteTelnet installed to reduce the local attack surface
• Implement endpoint protection solutions like SentinelOne to detect and prevent exploitation attempts
• Consider using alternative SSH client software until a patch is available
• Apply principle of least privilege to minimize the number of users who can access the affected application

# Verify installed AbsoluteTelnet version (Windows)
# Check program installation directory or application About dialog
# Upgrade to latest version from vendor website if running 11.12