T1021.005sub-technique of T1021 Remote Services
VNC
Linux · Windows · macOSnothing on this site yetT1021.005 on attack.mitre.org
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. VNC differs from Remote Desktop Protocol as VNC is screen-sharing software rather than resource-sharing software.
If this is happening now
Checklists and playbooks to open while the alert is still live.
Playbook for this stage
Cloud account compromise
Impossible travel, an unrecognised inbox rule, or a reported invoice-fraud attempt.
how MITRE says to see it
Behavioral Detection of Unauthorized VNC Remote Control Sessions
- Detection of VNC service or executable starting unexpectedly, followed by user session creation and interactive desktop activity (mouse/keyboard simulation).
- Spawning of VNC-related processes (e.g., `x11vnc`, `vncserver`) coupled with authentication logs and port listening behavior on TCP 5900.
- Detection of VNC-based remote control via `screensharingd` activity in Unified Logs along with concurrent remote login activity or suspicious user interaction.
what reduces it
- M1037 Filter Network Traffic. VNC defaults to TCP ports 5900 for the server, 5800 for browser access, and 5500 for a viewer in listening mode. Filtering or blocking these ports will inhibit VNC traffic utilizing default ports.
- M1033 Limit Software Installation. Restrict software installation to user groups that require it. A VNC server must be manually installed by the user or adversary.
- M1047 Audit. Inventory workstations for unauthorized VNC server software.
- M1042 Disable or Remove Feature or Program. Uninstall any VNC server software where not required.