Remote Services: VNC

Adversaries may use Valid Accounts to remotely control machines using Virtual Network Computing (VNC). The adversary may then perform actions as the logged-on user.

VNC is a desktop sharing system that allows users to remotely control another computer’s display by relaying mouse and keyboard inputs over the network. VNC does not necessarily use standard user credentials. Instead, a VNC client and server may be configured with sets of credentials that are used only for VNC connections.

ID: T1021.005
Sub-technique of:  T1021
Tactic: Lateral Movement
Platforms: Linux, Windows, macOS
System Requirements: VNC server installed and listening for connections.
Data Sources: Netflow/Enclave netflow, Network protocol analysis, Process use of network
CAPEC ID: CAPEC-555
Version: 1.0
Created: 11 February 2020
Last Modified: 23 March 2020

Procedure Examples

Name Description
GCMAN

GCMAN uses VNC for lateral movement.[3]

Proton

Proton uses VNC to connect into systems.[1]

ZxShell

ZxShell supports functionality for VNC sessions.[2]

Mitigations

Mitigation Description
Audit

Inventory workstations for unauthorized VNC server software.

Disable or Remove Feature or Program

Uninstall any VNC server software where not required.

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.

Limit Software Installation

Restrict software installation to user groups that require it. A VNC server must be manually installed by the user or adversary.

Detection

Use of VNC may be legitimate depending on the environment and how it’s used. Other factors, such as access patterns and activity that occurs after a remote login, may indicate suspicious or malicious behavior with VNC.

References