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 |
|---|---|---|---|---|---|
| amazon_virtual_private_cloud | Amazon Virtual Private Cloud | technique_scores | T1021.005 | VNC |
Comments
VPC security groups and network access control lists (NACLs) can be used to restrict direct access to remote services to trusted networks. This mitigates even an adversary with a valid account from accessing resources. This can be circumvented though if an adversary is able to compromise a trusted host and move laterally to a protected network. This results in an overall partial (coverage) score.
References
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| aws_network_firewall | AWS Network Firewall | technique_scores | T1021.005 | VNC |
Comments
AWS Network Firewall has the ability to pass, drop, or alert on traffic based on the network protocol as well as perform deep packet inspection on the payload. This functionality can be used to only allow remote services from trusted hosts (i.e., only allow remote access traffic from certain hosts). This mapping is given a score of Partial because even though it can restrict remote services traffic from untrusted hosts, it cannot protect against an adversary using a trusted host that is permitted to use remote services as part of an attack.
References
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