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Description

The following analytic identifies the use of svc-exe with Cobalt Strike. The behavior typically follows after an adversary has already gained initial access and is escalating privileges. Using svc-exe, a randomly named binary will be downloaded from the remote Teamserver and placed on disk within C:\Windows\400619a.exe. Following, the binary will be added to the registry under key HKLM\System\CurrentControlSet\Services\400619a\ with multiple keys and values added to look like a legitimate service. Upon loading, services.exe will spawn the randomly named binary from \\127.0.0.1\ADMIN$\400619a.exe. The process lineage is completed with 400619a.exe spawning rundll32.exe, which is the default spawnto_ value for Cobalt Strike. The spawnto_ value is arbitrary and may be any process on disk (typically system32/syswow64 binary). The spawnto_ process will also contain a network connection. During triage, review parallel procesess and identify any additional file modifications.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2021-05-18
  • Author: Michael Haag, Splunk
  • ID: c448488c-b7ec-11eb-8253-acde48001122

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1548 Abuse Elevation Control Mechanism Privilege Escalation, Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
CIS20
CVE 


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| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.parent_process_name=services.exe Processes.process_path=*admin$* by Processes.dest Processes.user Processes.parent_process Processes.process_name Processes.process Processes.process_id Processes.parent_process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `services_escalate_exe_filter`

Macros

The SPL above uses the following Macros:

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

Supported Add-on (TA)

List of Splunk Add-on’s tested to work with the analytic.

Required fields

List of fields required to use this analytic.

  • _time
  • Processes.dest
  • Processes.user
  • Processes.parent_process
  • Processes.process_name
  • Processes.process
  • Processes.process_id
  • Processes.parent_process_id

How To Implement

To successfully implement this search, you will need to ensure that DNS data is populating the Network_Resolution data model.

Known False Positives

False positives should be limited as services.exe should never spawn a process from ADMIN$. Filter as needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
76.0 80 95 A service process $parent_process_name$ with process path $process_path$ in host $dest$

: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

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