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Remote Services: VNC

ID Name
T1021.001 Remote Desktop Protocol
T1021.002 SMB/Windows Admin Shares
T1021.003 Distributed Component Object Model
T1021.004 SSH
T1021.005 VNC
T1021.006 Windows Remote Management
T1021.007 Cloud Services
T1021.008 Direct Cloud VM Connections

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.[1]

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.[2][3]

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.[4][5][6][7][8][9]

ID: T1021.005
Sub-technique of:  T1021
ⓘ
Tactic: Lateral Movement
ⓘ
Platforms: Linux, Windows, macOS
ⓘ
System Requirements: VNC server installed and listening for connections.
Version: 1.1
Created: 11 February 2020
Last Modified: 12 September 2024
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Procedure Examples

ID Name Description
S0484 Carberp

Carberp can start a remote VNC session by downloading a new plugin.[10]
S1014 DanBot

DanBot can use VNC for remote access to targeted systems.[11]
G0046 FIN7

FIN7 has used TightVNC to control compromised hosts.[12]
G0117 Fox Kitten

Fox Kitten has installed TightVNC server and client on compromised servers and endpoints for lateral movement.[13]
G0047 Gamaredon Group

Gamaredon Group has used VNC tools, including UltraVNC, to remotely interact with compromised hosts.[14][15][16]
G0036 GCMAN

GCMAN uses VNC for lateral movement.[17]
S1160 Latrodectus

Latrodectus has routed C2 traffic using Keyhole VNC.[18]
S0279 Proton

Proton uses VNC to connect into systems.[19]
S0266 TrickBot

TrickBot has used a VNC module to monitor the victim and collect information to pivot to valuable systems on the network [20][21]
S0670 WarzoneRAT

WarzoneRAT has the ability of performing remote desktop access via a VNC console.[22]
S0412 ZxShell

ZxShell supports functionality for VNC sessions.[23]

Mitigations

ID Mitigation Description
M1047 Audit

Inventory workstations for unauthorized VNC server software.
M1042 Disable or Remove Feature or Program

Uninstall any VNC server software where not required.
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.

Detection

ID Data Source Data Component Detects
DS0028 Logon Session Logon Session Creation

Monitor for user accounts logged into systems that may use Valid Accounts to remotely control machines using Virtual Network Computing (VNC). For example, on macOS systems log show --predicate 'process = "screensharingd" and eventMessage contains "Authentication:"' can be used to review incoming VNC connection attempts for suspicious activity.[24]

DS0029 Network Traffic Network Connection Creation

Monitor for newly constructed network connections that may use Valid Accounts to remotely control machines using Virtual Network Computing (VNC). 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 using VNC.

DS0009 Process Process Creation

Monitor for newly executed processes that may use Valid Accounts to remotely control machines using Virtual Network Computing (VNC). For example, on macOS systems the screensharingd process may be related to VNC connection activity.[24]

References

  1. T. Richardson, J. Levine, RealVNC Ltd.. (2011, March). The Remote Framebuffer Protocol. Retrieved September 20, 2021.
  2. Apple Support. (n.d.). Set up a computer running VNC software for Remote Desktop. Retrieved August 18, 2021.
  3. Tegan. (2019, August 15). Setting up System Authentication. Retrieved September 20, 2021.
  4. Z3RO. (2019, March 10). Day 70: Hijacking VNC (Enum, Brute, Access and Crack). Retrieved September 20, 2021.
  5. Nick Miles. (2017, November 30). Detecting macOS High Sierra root account without authentication. Retrieved September 20, 2021.
  6. Sergiu Gatlan. (2019, November 22). Dozens of VNC Vulnerabilities Found in Linux, Windows Solutions. Retrieved September 20, 2021.
  7. Offensive Security. (n.d.). VNC Authentication. Retrieved October 6, 2021.
  8. Administrator, Penetration Testing Lab. (2012, October 30). Attacking VNC Servers. Retrieved October 6, 2021.
  9. Jay Pipes. (2013, December 23). Security Breach! Tenant A is seeing the VNC Consoles of Tenant B!. Retrieved September 12, 2024.
  10. Giuliani, M., Allievi, A. (2011, February 28). Carberp - a modular information stealing trojan. Retrieved September 12, 2024.
  11. ClearSky Cyber Security . (2021, August). New Iranian Espionage Campaign By “Siamesekitten” - Lyceum. Retrieved June 6, 2022.
  12. Loui, E. and Reynolds, J. (2021, August 30). CARBON SPIDER Embraces Big Game Hunting, Part 1. Retrieved September 20, 2021.
  1. CISA. (2020, September 15). Iran-Based Threat Actor Exploits VPN Vulnerabilities. Retrieved December 21, 2020.
  2. Symantec. (2022, January 31). Shuckworm Continues Cyber-Espionage Attacks Against Ukraine. Retrieved February 17, 2022.
  3. Microsoft Threat Intelligence Center. (2022, February 4). ACTINIUM targets Ukrainian organizations. Retrieved February 18, 2022.
  4. Unit 42. (2022, February 3). Russia’s Gamaredon aka Primitive Bear APT Group Actively Targeting Ukraine. Retrieved February 21, 2022.
  5. Kaspersky Lab's Global Research & Analysis Team. (2016, February 8). APT-style bank robberies increase with Metel, GCMAN and Carbanak 2.0 attacks. Retrieved April 20, 2016.
  6. Unit 42. (2024, June 25). 2024-06-25-IOCs-from-Latrodectus-activity. Retrieved September 13, 2024.
  7. Patrick Wardle. (n.d.). Mac Malware of 2017. Retrieved September 21, 2018.
  8. Ionut Illascu. (2021, July 14). Trickbot updates its VNC module for high-value targets. Retrieved September 10, 2021.
  9. Radu Tudorica. (2021, July 12). A Fresh Look at Trickbot’s Ever-Improving VNC Module. Retrieved September 28, 2021.
  10. Harakhavik, Y. (2020, February 3). Warzone: Behind the enemy lines. Retrieved December 17, 2021.
  11. Allievi, A., et al. (2014, October 28). Threat Spotlight: Group 72, Opening the ZxShell. Retrieved September 24, 2019.
  12. Sarah Edwards. (2020, April 30). Analysis of Apple Unified Logs: Quarantine Edition [Entry 6] – Working From Home? Remote Logins. Retrieved August 19, 2021.