CVE-2021-47771: RDP Manager DoS Vulnerability

CVE-2021-47771 Overview

CVE-2021-47771 is a denial of service vulnerability affecting RDP Manager version 4.9.9.3. The vulnerability exists in connection input fields and allows local attackers to crash the application by adding oversized entries in the Verbindungsname (connection name) and Server fields. Successful exploitation results in a permanent freeze and crash of the software, potentially requiring full reinstallation.

Critical Impact

Local attackers can exploit improper input handling in RDP Manager to permanently crash the application, disrupting remote desktop management capabilities and potentially requiring complete software reinstallation.

Affected Products

• RDP Manager 4.9.9.3

Discovery Timeline

• 2026-01-15 - CVE CVE-2021-47771 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2021-47771

Vulnerability Analysis

This denial of service vulnerability stems from improper handling of resource consumption in the RDP Manager application. The vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling), indicating that the application fails to properly limit or manage the size of input data in connection configuration fields.

The attack requires local access to the system where RDP Manager is installed. An attacker with low privileges can exploit this vulnerability without any user interaction. While the vulnerability does not impact confidentiality or integrity, it has a high impact on availability, causing the application to become completely unresponsive.

Root Cause

The root cause is improper input validation and resource allocation in RDP Manager's connection management functionality. The application does not implement adequate bounds checking or size limits on the Verbindungsname and Server input fields. When excessively large data is entered into these fields, the application fails to handle the resource allocation properly, leading to memory exhaustion or buffer-related issues that cause the application to freeze and crash.

Attack Vector

The attack is conducted locally by a user with access to the RDP Manager application. The attacker manipulates the connection configuration interface by entering oversized strings into the connection name and server fields. The application's failure to validate input length results in resource exhaustion, causing a denial of service condition.

The exploitation is straightforward and does not require sophisticated technical knowledge. An attacker simply needs to add connections with excessively long field values through the normal user interface. Once triggered, the crash condition persists, potentially requiring complete reinstallation of the software to restore functionality.

Technical details and proof-of-concept information can be found in the Exploit-DB #50484 and Vulnerability Lab ID #2309 references.

Detection Methods for CVE-2021-47771

Indicators of Compromise

• Unexplained crashes or freezes of RDP Manager application
• Abnormally large configuration files for RDP Manager connection settings
• Connection entries with unusually long names or server addresses in RDP Manager configuration
• Application event logs showing memory exhaustion or resource allocation failures related to RDP Manager

Detection Strategies

• Monitor for crashes of the RDP Manager process (RDPManager.exe) and investigate the application state prior to termination
• Implement application whitelisting and behavioral monitoring to detect unusual application behavior patterns
• Use SentinelOne's behavioral AI to identify anomalous resource consumption patterns in endpoint applications
• Review RDP Manager configuration files for entries with excessively long field values

Monitoring Recommendations

• Enable crash reporting and application telemetry for RDP Manager installations
• Implement endpoint detection and response (EDR) solutions to monitor application stability
• Configure alerts for repeated application crashes or resource exhaustion events
• Monitor system resource usage for spikes associated with RDP Manager processes

How to Mitigate CVE-2021-47771

Immediate Actions Required

• Restrict access to RDP Manager to trusted users only
• Implement least privilege principles for systems running RDP Manager
• Back up existing RDP Manager configurations before any remediation attempts
• Consider migrating to alternative remote desktop management solutions with better input validation
• Monitor for any signs of exploitation attempts on affected systems

Patch Information

No vendor patch information is currently available in the NVD database. The vendor's download page can be referenced at the C Inspiration Download Resource (archived). Organizations should check with the vendor for updated versions that address this vulnerability.

Workarounds

• Limit physical and remote access to systems with RDP Manager installed to trusted personnel only
• Implement application-level controls to restrict configuration changes
• Consider using group policies or endpoint management solutions to lock down RDP Manager settings
• Deploy monitoring solutions to detect and alert on application crashes
• Evaluate alternative RDP management tools that implement proper input validation

Organizations should implement access controls to limit who can modify RDP Manager connection configurations. Consider restricting write access to configuration files and implementing change management procedures for connection settings.