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Description

This detection targets behaviors observed in post exploit kits like Meterpreter and Koadic that are run in memory. We have observed that these tools must invoke an excessive number of taskhost.exe and taskhostex.exe processes to complete various actions (discovery, lateral movement, etc.). It is extremely uncommon in the course of normal operations to see so many distinct taskhost and taskhostex processes running concurrently in a short time frame.

Annotations

ATT&CK
ID Technique Tactic
T1059 Command and Scripting Interpreter Execution
Kill Chain Phase
  • Exploitation
NIST
CIS20
CVE
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| tstats `security_content_summariesonly` values(Processes.process_id) as process_ids  min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Processes WHERE Processes.process_name = "taskhost.exe" OR Processes.process_name = "taskhostex.exe" BY Processes.dest Processes.process_name _time span=1h 
| `drop_dm_object_name(Processes)` 
| eval pid_count=mvcount(process_ids) 
| eval taskhost_count_=if(process_name == "taskhost.exe", pid_count, 0) 
| eval taskhostex_count_=if(process_name == "taskhostex.exe", pid_count, 0) 
| stats sum(taskhost_count_) as taskhost_count, sum(taskhostex_count_) as taskhostex_count by _time, dest, firstTime, lastTime 
| where taskhost_count > 10 and taskhostex_count > 10 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `excessive_number_of_taskhost_processes_filter`

Macros

The SPL above uses the following Macros:

Note that excessive_number_of_taskhost_processes_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
  • Processes.process_id
  • Processes.process_name
  • Processes.dest
  • Processes.user

How To Implement

To successfully implement this search you need to be ingesting events related to processes on the endpoints that include the name of the process and process id into the Endpoint datamodel in the Processes node.

Known False Positives

Administrators, administrative actions or certain applications may run many instances of taskhost and taskhostex concurrently. Filter as needed.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
56.0 80 70 An excessive amount of $process_name$ was executed on $dest$ indicative of suspicious behavior.

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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