LoFP / system administrators may use looks like psexec for troubleshooting or administrations tasks. however, this will typically come only from certain users and certain systems that can be added to an allow list.

Techniques

• T1021
• T1021.002

Sample rules

Executable File Written in Administrative SMB Share

• source: splunk
• technicques:
  • T1021
  • T1021.002

Description

The following analytic identifies executable files (.exe or .dll) being written to Windows administrative SMB shares (Admin$, IPC$, C$). This represents suspicious behavior as its commonly used by tools like PsExec/PaExec and others to stage service binaries before creating and starting a Windows service on remote endpoints. Red Teams and adversaries alike may abuse administrative shares for lateral movement and remote code execution. The Trickbot malware family also implements this behavior to try to infect other machines in the infected network.

Detection logic

`wineventlog_security` EventCode=5145 RelativeTargetName IN ("*.exe","*.dll") ObjectType=File ShareName IN ("\\\\*\\C$","\\\\*\\IPC$","\\\\*\\admin$") AccessMask= "0x2" 
| stats min(_time) as firstTime max(_time) as lastTime count by EventCode ShareName RelativeTargetName ObjectType AccessMask src_user src_port IpAddress 
| `security_content_ctime(firstTime)`  
| `executable_file_written_in_administrative_smb_share_filter`