CVE-2021-47891 in Unified Remote
Summary
by MITRE • 01/23/2026
Unified Remote 3.9.0.2463 contains a remote code execution vulnerability that allows attackers to send crafted network packets to execute arbitrary commands. Attackers can exploit the service by connecting to port 9512 and sending specially crafted packets to open a command prompt and download and execute malicious payloads.
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Analysis
by VulDB Data Team • 01/23/2026
The vulnerability identified as CVE-2021-47891 represents a critical remote code execution flaw within Unified Remote version 3.9.0.2463, a remote desktop and control application designed for Windows systems. This vulnerability exposes the application to malicious network exploitation through its listening service on port 9512, creating a significant security risk for organizations that deploy this software without proper network segmentation or access controls. The flaw stems from inadequate input validation and sanitization within the application's network communication protocol implementation, allowing attackers to craft malicious packets that bypass normal authentication mechanisms and execute arbitrary commands on the target system.
The technical implementation of this vulnerability involves the application's failure to properly validate incoming network packets received on the designated port 9512. Attackers can exploit this weakness by establishing a connection to the service and transmitting specially crafted data structures that trigger buffer overflow conditions or command injection vulnerabilities within the application's processing logic. This allows unauthorized users to gain command execution privileges on the affected system, effectively providing them with a backdoor that can be used to download additional malware, establish persistence mechanisms, or conduct further reconnaissance activities. The vulnerability operates at the application layer of the network stack, making it particularly dangerous as it requires no authentication or prior access to the system.
The operational impact of CVE-2021-47891 extends beyond simple command execution, as it enables attackers to establish persistent access to compromised systems and potentially escalate privileges to system-level access. Organizations running Unified Remote without proper network controls face significant risk of lateral movement within their networks, as the compromised system can serve as a pivot point for attacking other networked devices. The vulnerability's remote nature means that attackers can exploit it from anywhere on the internet, provided they can reach the target system on port 9512, making it particularly attractive to threat actors seeking to compromise systems without physical access or prior knowledge of internal network configurations.
Security practitioners should implement immediate mitigations including network segmentation to restrict access to port 9512, deployment of network firewalls to block external access to this port, and mandatory application whitelisting policies to prevent unauthorized execution of the Unified Remote service. The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and demonstrates characteristics consistent with ATT&CK technique T1059.001 for command and script interpreter execution. Organizations should also consider implementing intrusion detection systems to monitor for suspicious network traffic patterns associated with this specific vulnerability and ensure timely patch deployment through official vendor channels. The risk assessment should include network scanning to identify affected systems and implementation of continuous monitoring procedures to detect potential exploitation attempts.
This vulnerability highlights the importance of proper input validation and secure coding practices in network services, particularly those that operate with elevated privileges or execute system commands. The flaw represents a classic example of how insufficient security controls in network protocols can lead to complete system compromise, emphasizing the need for comprehensive security testing including penetration testing and vulnerability assessments of network services before deployment in production environments. Organizations should also consider implementing zero-trust network architectures that minimize the attack surface and reduce the impact of similar vulnerabilities by limiting lateral movement capabilities and enforcing strict access controls.