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Spoolsv suspicious loaded modules

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Some attacks such as PrintNightmare perform module loads into Spoolsv.exe based on dll loading from a specific path. This search detects the loaded modules made by spoolsv.exe after the exploitation.

Procedure

  1. Ensure you have at least version 6.0.4.
  2. Run the following search. You can optimize it by specifying an index and adjusting the time range.
sourcetype=XmlWinEventLog:Microsoft-Windows-Sysmon/Operational OR source=XmlWinEventLog:Microsoft-Windows-Sysmon/Operational 
EventCode=7 Image ="*\\spoolsv.exe" ImageLoaded="*\\Windows\\System32\\spool\\drivers\\x64\\*"
ImageLoaded = "*.dll" 
| stats dc(ImageLoaded) AS countImgloaded values(ImageLoaded) AS ImgLoaded count min(_time) AS firstTime max(_time) AS lastTime BY Image Computer EventCode 
| where countImgloaded >= 3

Search explanation

The table provides an explanation of what each part of this search achieves. You can adjust this query based on the specifics of your environment.

Splunk Search Explanation
sourcetype=XmlWinEventLog:Microsoft-Windows-Sysmon/Operational OR 
source=XmlWinEventLog:Microsoft-Windows-Sysmon/Operational		 Search Sysmon operational data.
EventCode=7 Search for when a module is loaded in a specific process.
Image ="*\\spoolsv.exe" ImageLoaded="*\\Windows\\System32\\spool\\drivers\\x64\\*" ImageLoaded = "*.dll" Search for modules related to spoolsv.exe.
| stats dc(ImageLoaded) AS countImgloaded values(ImageLoaded) AS ImgLoaded count min(_time) AS firstTime max(_time) AS lastTime BY Image Computer EventCode  Return the number of times each distinct image was loaded, the name of image loaded, and the first and last time each image was loaded, renaming the fields as shown. Then  sort the results by the computer and the event code.
 
| where countImgloaded >= 3 Return results only when 3 or more modules are loaded by the exploit (unidrv.dll, kernelbase.dll, and the suspect dll) at the same time in the specific target folder. 

Next steps

Ensure you filter for false positives on this search. 

During triage, isolate the endpoint and review for source of exploitation. Capture any additional file modification events.

If your results indicate an attack has occurred, the host or computer where the vulnerability is detected needs to be further investigated and remediated according to your response plan. This involves a final step of re-imaging the system with a known good system build after investigation.

Finally, you might be interested in other processes associated with the Detecting print spooler attacks use case.