splunk-security_content/docs/_posts/2021-07-01-spoolsv_spawning_rundll32.md

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title	excerpt	categories	last_modified_at	toc	toc_label	tags
Spoolsv Spawning Rundll32	Print Processors, Boot or Logon Autostart Execution	Endpoint	2021-07-01	true		Print Processors Persistence Privilege Escalation Boot or Logon Autostart Execution Persistence Privilege Escalation Splunk Enterprise Splunk Enterprise Security Splunk Cloud CVE-2021-34527 Endpoint

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Description

The following analytic identifies a suspicious child process, rundll32.exe, with no command-line arguments being spawned from spoolsv.exe. This was identified during our testing of CVE-2021-34527 previously (CVE-2021-1675) or PrintNightmare. Typically, this is not normal behavior for spoolsv.exe to spawn a process. During triage, isolate the endpoint and review for source of exploitation. Capture any additional file modification events.

• Type: TTP
• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
• Datamodel: Endpoint
• Last Updated: 2021-07-01
• Author: Mauricio Velazco, Michael Haag, Splunk
• ID: 15d905f6-da6b-11eb-ab82-acde48001122

ATT&CK

ID	Technique	Tactic
T1547.012	Print Processors	Persistence, Privilege Escalation

| T1547 | Boot or Logon Autostart Execution | Persistence, Privilege Escalation |

Search

| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.parent_process_name=spoolsv.exe `process_rundll32` by Processes.dest Processes.user Processes.parent_process Processes.original_file_name 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)` 
| `spoolsv_spawning_rundll32_filter`

Macros

The SPL above uses the following Macros:

• process_rundll32
• security_content_ctime
• security_content_summariesonly

Note that spoolsv_spawning_rundll32_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.dest
• Processes.user
• Processes.parent_process_name
• Processes.parent_process
• Processes.original_file_name
• Processes.process_name
• Processes.process
• Processes.process_id
• Processes.parent_process_path
• Processes.process_path
• Processes.parent_process_id

How To Implement

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Processes node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Known False Positives

Limited false positives have been identified. There are limited instances where rundll32.exe may be spawned by a legitimate print driver.

Associated Analytic story

• PrintNightmare CVE-2021-34527

Kill Chain Phase

• Exploitation

RBA

Risk Score	Impact	Confidence	Message
72.0	80	90	parent_process has spawned process_name on endpoint ComputerName. This behavior is suspicious and related to PrintNightmare.

Note that risk score is calculated base on the following formula: (Impact * Confidence)/100

CVE

ID	Summary	CVSS
CVE-2021-34527	Windows Print Spooler Remote Code Execution Vulnerability	9.0

Reference

• https://blog.truesec.com/2021/06/30/fix-for-printnightmare-cve-2021-1675-exploit-to-keep-your-print-servers-running-while-a-patch-is-not-available/
• https://blog.truesec.com/2021/06/30/exploitable-critical-rce-vulnerability-allows-regular-users-to-fully-compromise-active-directory-printnightmare-cve-2021-1675/
• https://www.reddit.com/r/msp/comments/ob6y02/critical_vulnerability_printnightmare_exposes

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

• https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1547.012/printnightmare/windows-sysmon.log

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