Adversaries may use Valid Accounts to remotely control machines using Virtual Network Computing (VNC). VNC is a platform-independent desktop sharing system that uses the RFB (“remote framebuffer”) protocol to enable users to remotely control another computer’s display by relaying the screen, mouse, and keyboard inputs over the network.(Citation: The Remote Framebuffer Protocol)
VNC differs from Remote Desktop Protocol as VNC is screen-sharing software rather than resource-sharing software. By default, VNC uses the system's authentication, but it can be configured to use credentials specific to VNC.(Citation: MacOS VNC software for Remote Desktop)(Citation: VNC Authentication)
Adversaries may abuse VNC to perform malicious actions as the logged-on user such as opening documents, downloading files, and running arbitrary commands. An adversary could use VNC to remotely control and monitor a system to collect data and information to pivot to other systems within the network. Specific VNC libraries/implementations have also been susceptible to brute force attacks and memory usage exploitation.(Citation: Hijacking VNC)(Citation: macOS root VNC login without authentication)(Citation: VNC Vulnerabilities)(Citation: Offensive Security VNC Authentication Check)(Citation: Attacking VNC Servers PentestLab)(Citation: Havana authentication bug)
View in MITRE ATT&CK®| Capability ID | Capability Description | Mapping Type | ATT&CK ID | ATT&CK Name | Notes |
|---|---|---|---|---|---|
| CIS-2.3 | Address Unauthorized Software | mitigates | T1021.005 | VNC |
Comments
Adversaries use VNC server software to establish remote interactive access to systems. When VNC server software is classified as unauthorized, this safeguard requires it to be removed, eliminating the VNC server endpoint required to establish the remote session.
References
|
| CIS-13.4 | Perform Traffic Filtering Between Network Segments | mitigates | T1021.005 | VNC |
Comments
Filter or block VNC traffic across network-segment boundaries, including commonly used VNC ports, except where the communication is explicitly required.
References
|
| CIS-4.8 | Uninstall or Disable Unnecessary Services on Enterprise Assets and Software | mitigates | T1021.005 | VNC |
Comments
Uninstalling unnecessary VNC server software removes the listener and prevents remote control through that implementation.
References
|
| CIS-4.6 | Securely Manage Enterprise Assets and Software | mitigates | T1021.005 | VNC |
Comments
Secure management can prohibit unencrypted VNC deployments or require encrypted tunnels and approved administrative tooling. The relationship is partial because some VNC implementations or tunnels remain accessible with valid credentials.
References
|
| CIS-4.5 | Implement and Manage a Firewall on End-User Devices | mitigates | T1021.005 | VNC |
Comments
VNC requires an accessible listener, commonly on TCP 5900 and related ports. Blocking those ports unless specifically authorized directly prevents unauthorized VNC access.
References
|
| CIS-4.4 | Implement and Manage a Firewall on Servers | mitigates | T1021.005 | VNC |
Comments
A server firewall prevents unauthorized inbound VNC connections unless the relevant service and source systems are explicitly permitted.
References
|