Try in Splunk Security Cloud

Description

The following analytic identifies instances of mshta.exe writing files to world-writable directories. It leverages Sysmon EventCode 11 logs to detect file write operations by mshta.exe to directories like C:\Windows\Tasks and C:\Windows\Temp. This activity is significant as it often indicates an attempt to establish persistence or execute malicious code, deviating from the utility's legitimate use. If confirmed malicious, this behavior could lead to the execution of multi-stage payloads, potentially resulting in full system compromise and unauthorized access to sensitive information.

  • Type: TTP

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

  • Last Updated: 2024-05-26
  • Author: Michael Haag, Splunk
  • ID: efbcf8ee-bc75-47f1-8985-a5c638c4faf0

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1218.005 Mshta Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


1
2
3
4
5
6



`sysmon` EventCode=11 Image="*\\mshta.exe" TargetFilename IN ("*\\Windows\\Tasks\\*", "*\\Windows\\Temp\\*", "*\\Windows\\tracing\\*", "*\\Windows\\PLA\\Reports\\*", "*\\Windows\\PLA\\Rules\\*", "*\\Windows\\PLA\\Templates\\*", "*\\Windows\\PLA\\Reports\\en-US\\*", "*\\Windows\\PLA\\Rules\\en-US\\*", "*\\Windows\\Registration\\CRMLog\\*", "*\\Windows\\System32\\Tasks\\*", "*\\Windows\\System32\\Com\\dmp\\*", "*\\Windows\\System32\\LogFiles\\WMI\\*", "*\\Windows\\System32\\Microsoft\\Crypto\\RSA\\MachineKeys\\*", "*\\Windows\\System32\\spool\\PRINTERS\\*", "*\\Windows\\System32\\spool\\SERVERS\\*", "*\\Windows\\System32\\spool\\drivers\\color\\*", "*\\Windows\\System32\\Tasks\\Microsoft\\Windows\\RemoteApp and Desktop Connections Update\\*", "*\\Windows\\SysWOW64\\Tasks\\*", "*\\Windows\\SysWOW64\\Com\\dmp\\*", "*\\Windows\\SysWOW64\\Tasks\\Microsoft\\Windows\\PLA\\*", "*\\Windows\\SysWOW64\\Tasks\\Microsoft\\Windows\\RemoteApp and Desktop Connections Update\\*", "*\\Windows\\SysWOW64\\Tasks\\Microsoft\\Windows\\PLA\\System\\*") 
| rename Computer as dest, User as user 
| stats count min(_time) as firstTime max(_time) as lastTime by dest, user, Image, TargetFilename 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `windows_mshta_writing_to_world_writable_path_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_mshta_writing_to_world_writable_path_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.

  • dest
  • user
  • Image
  • TargetFilename

How To Implement

The analytic is designed to be run against Sysmon event logs collected from endpoints. The analytic requires the Sysmon event logs to be ingested into Splunk. The search focuses on EventCode 11 where the Image is mshta.exe and the TargetFilename is within world-writable directories such as C:\Windows\Tasks, C:\Windows\Temp, and others. The detection is designed to catch the initial file write operation by mshta.exe to these locations, which is indicative of an attempt to establish persistence or execute malicious code. The analytic can be modified to include additional world-writable directories as needed.

Known False Positives

False positives may occur if legitimate processes are writing to world-writable directories. It is recommended to investigate the context of the file write operation to determine if it is malicious or not. Modify the search to include additional known good paths for mshta.exe to reduce false positives.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
64.0 80 80 An instance of $Image$ writing to $TargetFilename$ was detected on $dest$.

: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

source | version: 2