CVE-2021-47759: MTPutty Information Disclosure Flaw

CVE-2021-47759 Overview

CVE-2021-47759 is a sensitive information disclosure vulnerability affecting MTPutty version 1.0.1.21. This vulnerability allows local attackers to view SSH connection passwords through Windows PowerShell process listing. By executing a PowerShell command to retrieve the full command line of MTPutty processes, attackers can expose plaintext SSH credentials, potentially compromising remote systems and network infrastructure.

Critical Impact

Local attackers can harvest SSH credentials in plaintext by simply querying Windows process information, enabling unauthorized access to remote systems managed through MTPutty.

Affected Products

• MTPutty 1.0.1.21
• TTYPlus Multi-Tabbed PuTTY Tool

Discovery Timeline

• 2026-01-15 - CVE CVE-2021-47759 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2021-47759

Vulnerability Analysis

This vulnerability falls under CWE-522 (Insufficiently Protected Credentials), where MTPutty fails to adequately protect sensitive authentication information during SSH session initialization. When MTPutty establishes an SSH connection, it passes credentials including passwords as command-line arguments to the underlying PuTTY process. These command-line arguments are visible to any local user with sufficient privileges to query process information on the Windows system.

The fundamental issue is the insecure handling of sensitive credentials in process memory and command-line parameters. Windows maintains process command-line information in a manner accessible through standard system APIs and utilities, meaning any user with local access can potentially enumerate running processes and their associated command lines.

Root Cause

The root cause of this vulnerability is MTPutty's design decision to pass SSH credentials, including passwords, as plaintext command-line arguments when spawning SSH connection processes. This architectural flaw violates secure credential handling principles, as command-line arguments in Windows are stored in process memory regions that can be accessed by other processes and users on the system.

Rather than using secure credential storage mechanisms, environment variables with restricted permissions, or inter-process communication channels, MTPutty directly exposes passwords in the process command line where they can be harvested by any local attacker.

Attack Vector

The attack is performed locally and requires the attacker to have low-privilege access to the same Windows system where MTPutty is running. The attacker can leverage native Windows PowerShell commands or WMI queries to enumerate process command lines and extract plaintext SSH credentials.

The exploitation technique involves querying the Windows Management Instrumentation (WMI) Win32_Process class to retrieve the CommandLine property of running MTPutty processes. This technique requires no special tools or elevated privileges beyond basic local user access, making it trivially exploitable in shared computing environments or systems compromised through other means.

Technical details and proof-of-concept information can be found in the Exploit-DB #50574 advisory.

Detection Methods for CVE-2021-47759

Indicators of Compromise

• Unusual PowerShell or WMI queries targeting process command-line enumeration
• Evidence of credential harvesting scripts or tools in user directories
• Unexpected access to systems that were previously accessed only via MTPutty SSH connections
• Process monitoring alerts for Get-WmiObject or Get-CimInstance calls targeting Win32_Process

Detection Strategies

• Monitor for PowerShell commands that query Win32_Process CommandLine properties
• Implement endpoint detection rules for process enumeration techniques commonly used in credential harvesting
• Deploy security controls that alert on bulk process information queries
• Review authentication logs for unauthorized SSH connections using harvested credentials

Monitoring Recommendations

• Enable PowerShell script block logging and module logging to capture credential harvesting attempts
• Configure Windows Security Event logging for process creation events (Event ID 4688) with command-line auditing
• Implement user behavior analytics to detect unusual process enumeration activity
• Monitor for suspicious lateral movement following potential credential exposure

How to Mitigate CVE-2021-47759

Immediate Actions Required

• Replace MTPutty with an alternative SSH client that does not expose credentials in command-line arguments
• Review and rotate any SSH credentials that may have been used with MTPutty 1.0.1.21
• Implement SSH key-based authentication instead of password-based authentication where possible
• Restrict local access to systems running MTPutty to minimize exposure

Patch Information

No vendor patch information is currently available for this vulnerability. Users are advised to monitor the TTYPlus Multi-Tabbed PuTTY Tool website for security updates. Given the architectural nature of this vulnerability, users should consider migrating to alternative SSH management tools that implement secure credential handling.

Workarounds

• Transition to SSH key-based authentication to eliminate password exposure in command lines
• Use alternative SSH clients that do not expose credentials in process arguments
• Implement strict access controls to limit local user access on systems running MTPutty
• Consider using Windows Credential Guard or similar credential protection mechanisms where available
• Segment networks to limit the impact of potential credential compromise

# Generate SSH key pair as password-free alternative
ssh-keygen -t ed25519 -f ~/.ssh/mtputty_replacement_key -N ""

# Copy public key to remote servers
ssh-copy-id -i ~/.ssh/mtputty_replacement_key.pub user@remote-host

# Use key-based authentication instead of passwords
ssh -i ~/.ssh/mtputty_replacement_key user@remote-host