Remote Desktop Protocol
Remote desktop is a common feature in operating systems. It allows a user to log into an interactive session with a system desktop graphical user interface on a remote system. Microsoft refers to its implementation of the Remote Desktop Protocol (RDP) as Remote Desktop Services (RDS). (Citation: TechNet Remote Desktop Services) There are other implementations and third-party tools that provide graphical access Remote Services similar to RDS.
Adversaries may connect to a remote system over RDP/RDS to expand access if the service is enabled and allows access to accounts with known credentials. Adversaries will likely use Credential Access techniques to acquire credentials to use with RDP. Adversaries may also use RDP in conjunction with the Accessibility Features technique for Persistence. (Citation: Alperovitch Malware)
Adversaries may also perform RDP session hijacking which involves stealing a legitimate user's remote session. Typically, a user is notified when someone else is trying to steal their session and prompted with a question. With System permissions and using Terminal Services Console, c:\windows\system32\tscon.exe session number to be stolen], an adversary can hijack a session without the need for credentials or prompts to the user. (Citation: RDP Hijacking Korznikov) This can be done remotely or locally and with active or disconnected sessions. (Citation: RDP Hijacking Medium) It can also lead to [Remote System Discovery and Privilege Escalation by stealing a Domain Admin or higher privileged account session. All of this can be done by using native Windows commands, but it has also been added as a feature in RedSnarf. (Citation: Kali Redsnarf)
Mitigations |
|
| Mitigation | Description |
|---|---|
| Audit |
Perform audits or scans of systems, permissions, insecure software, insecure configurations, etc. to identify potential weaknesses. |
| Remote Desktop Protocol Mitigation |
Disable the RDP service if it is unnecessary, remove unnecessary accounts and groups from Remote Desktop Users groups, and enable firewall rules to block RDP traffic between network security zones. Audit the Remote Desktop Users group membership regularly. Remove the local Administrators group from the list of groups allowed to log in through RDP. Limit remote user permissions if remote access is necessary. Use remote desktop gateways and multifactor authentication for remote logins. (Citation: Berkley Secure) Do not leave RDP accessible from the internet. Change GPOs to define shorter timeouts sessions and maximum amount of time any single session can be active. Change GPOs to specify the maximum amount of time that a disconnected session stays active on the RD session host server. (Citation: Windows RDP Sessions) |
| Limit Access to Resource Over Network |
Prevent access to file shares, remote access to systems, unnecessary services. Mechanisms to limit access may include use of network concentrators, RDP gateways, etc. |
| Multi-factor Authentication |
Use two or more pieces of evidence to authenticate to a system; such as username and password in addition to a token from a physical smart card or token generator. |
| Privileged Account Management |
Manage the creation, modification, use, and permissions associated to privileged accounts, including SYSTEM and root. |
| Operating System Configuration |
Make configuration changes related to the operating system or a common feature of the operating system that result in system hardening against techniques. |
| User Account Management |
Manage the creation, modification, use, and permissions associated to user accounts. |
| Network Segmentation |
Architect sections of the network to isolate critical systems, functions, or resources. Use physical and logical segmentation to prevent access to potentially sensitive systems and information. Use a DMZ to contain any internet-facing services that should not be exposed from the internal network. Configure separate virtual private cloud (VPC) instances to isolate critical cloud systems. |
| Disable or Remove Feature or Program |
Remove or deny access to unnecessary and potentially vulnerable software to prevent abuse by adversaries. |
Detection
Use of RDP may be legitimate, depending on the network environment and how it is used. Other factors, such as access patterns and activity that occurs after a remote login, may indicate suspicious or malicious behavior with RDP. Monitor for user accounts logged into systems they would not normally access or access patterns to multiple systems over a relatively short period of time.
Also, set up process monitoring for tscon.exe usage and monitor service creation that uses cmd.exe /k or cmd.exe /c in its arguments to prevent RDP session hijacking.
References
- Berkeley Security, University of California. (n.d.). Securing Remote Desktop for System Administrators. Retrieved November 4, 2014.
- Microsoft. (n.d.). Configure Timeout and Reconnection Settings for Remote Desktop Services Sessions. Retrieved December 11, 2017.
- NCC Group PLC. (2016, November 1). Kali Redsnarf. Retrieved December 11, 2017.
- Beaumont, K. (2017, March 19). RDP hijacking — how to hijack RDS and RemoteApp sessions transparently to move through an organisation. Retrieved December 11, 2017.
- Korznikov, A. (2017, March 17). Passwordless RDP Session Hijacking Feature All Windows versions. Retrieved December 11, 2017.
- Alperovitch, D. (2014, October 31). Malware-Free Intrusions. Retrieved November 4, 2014.
- Microsoft. (n.d.). Remote Desktop Services. Retrieved June 1, 2016.
Связанные риски
Каталоги
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