Executable File Written in Administrative SMB Share

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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 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: 2024-02-14
• Author: Teoderick Contreras, Mauricio Velazco, Splunk
• ID: f63c34fe-a435-11eb-935a-acde48001122

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1021	Remote Services	Lateral Movement

T1021.002

SMB/Windows Admin Shares

Lateral Movement

Kill Chain Phase

• Exploitation

NIST

• DE.CM

CIS20

• CIS 10

CVE

Search

`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`

Macros

The SPL above uses the following Macros:

• security_content_ctime
• wineventlog_security

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 fields

List of fields required to use this analytic.

• _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

• Active Directory Lateral Movement
• Prestige Ransomware
• Graceful Wipe Out Attack
• Industroyer2
• IcedID
• Data Destruction
• Hermetic Wiper
• Trickbot

RBA

Risk Score	Impact	Confidence	Message
70.0	70	100	$src_user$ dropped or created an executable file in known sensitive SMB share. Share name=$ShareName$, Target name=$RelativeTargetName$, and Access mask=$AccessMask$

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

• https://attack.mitre.org/techniques/T1021/002/
• https://www.rapid7.com/blog/post/2013/03/09/psexec-demystified/
• https://labs.vipre.com/trickbot-and-its-modules/
• https://whitehat.eu/incident-response-case-study-featuring-ryuk-and-trickbot-part-2/
• https://thedfirreport.com/2023/05/22/icedid-macro-ends-in-nokoyawa-ransomware/

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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