RDP Sensitive Settings Changed to Zero
Detects tampering of RDP Terminal Service/Server sensitive settings. Such as allowing unauthorized users access to a system via the 'fAllowUnsolicited' or enabling RDP via 'fDenyTSConnections', etc.
Convert In Phoenix Studio
Open this Sigma rule in the converter with the YAML preloaded and ready for backend selection.
detection:
selection:
TargetObject|endswith:
- '\fDenyTSConnections' # Specifies whether Remote Desktop connections are enabled - When set to zero RDP is enabled
- '\fSingleSessionPerUser' # When changed to 0 it allows multiple RDP sessions
- '\UserAuthentication' # Specifies that Network-Level user authentication is not required before the remote desktop connection is established
Details: 'DWORD (0x00000000)'
condition: selectionSome of the keys mentioned here could be modified by an administrator while setting group policy (it should be investigated either way)
Techniques
RDP Sensitive Settings Changed
Detects tampering of RDP Terminal Service/Server sensitive settings. Such as allowing unauthorized users access to a system via the 'fAllowUnsolicited' or enabling RDP via 'fDenyTSConnections', etc. Below is a list of registry keys/values that are monitored by this rule: - Shadow: Used to enable Remote Desktop shadowing, which allows an administrator to view or control a user's session. - DisableRemoteDesktopAntiAlias: Disables anti-aliasing for remote desktop sessions. - DisableSecuritySettings: Disables certain security settings for Remote Desktop connections. - fAllowUnsolicited: Allows unsolicited remote assistance offers. - fAllowUnsolicitedFullControl: Allows unsolicited remote assistance offers with full control. - InitialProgram: Specifies a program to run automatically when a user logs on to a remote computer. - ServiceDll: Used in RDP hijacking techniques to specify a custom DLL to be loaded by the Terminal Services service. - SecurityLayer: Specifies the security layer used for RDP connections.
Detects similar activity. Both rules may fire on overlapping events.
RDP Enable or Disable via Win32_TerminalServiceSetting WMI Class
Detects enabling or disabling of Remote Desktop Protocol (RDP) using alternate methods such as WMIC or PowerShell. In PowerShell one-liner commands, the "SetAllowTSConnections" method of the "Win32_TerminalServiceSetting" class may be used to enable or disable RDP. In WMIC, the "rdtoggle" alias or "Win32_TerminalServiceSetting" class may be used for the same purpose.
Detects similar activity. Both rules may fire on overlapping events.