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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 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.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2021-11-18
  • Author: Teoderick Contreras, Mauricio Velazco, Splunk
  • ID: f63c34fe-a435-11eb-935a-acde48001122

Annotations

ATT&CK
ID Technique Tactic
T1021 Remote Services Lateral Movement
T1021.002 SMB/Windows Admin Shares Lateral Movement
Kill Chain Phase
  • Exploitation
NIST
CIS20
CVE
1
2
3
4
5
`wineventlog_security` EventCode=5145 Relative_Target_Name IN ("*.exe","*.dll") Object_Type=File Share_Name IN ("\\\\*\\C$","\\\\*\\IPC$","\\\\*\\admin$") Access_Mask= "0x2" 
| stats min(_time) as firstTime max(_time) as lastTime count by EventCode Share_Name Relative_Target_Name Object_Type Access_Mask user src_port Source_Address 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `executable_file_written_in_administrative_smb_share_filter`

Macros

The SPL above uses the following Macros:

:information_source: executable_file_written_in_administrative_smb_share_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required field

  • _time
  • EventCode
  • Share_Name
  • Relative_Target_Name
  • Object_Type
  • Access_Mask
  • user
  • src_port
  • Source_Address

How To Implement

To successfully implement this search, you need to be ingesting Windows Security Event Logs with 5145 EventCode enabled. The Windows TA is also required. Also enable the object Audit access success/failure in your group policy.

Known False Positives

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.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
70.0 70 100 $user$ dropped or created an executable file in known sensitive SMB share. Share name=$Share_Name$, Target name=$Relative_Target_Name$, and Access mask=$Access_Mask$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

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