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Splunk Lantern

Spoolsv suspicious process access

 

Some attacks such as PrintNightmare take advantage of a critical Windows Print Spooler Vulnerability to gain privilege escalation on the vulnerable machine. This search looks for suspicious process access made by the spoolsv.exe that may be related to the attack.

Procedure

  1. Ensure you have at least version 6.0.4. Tune and filter known instances of spoolsv.exe.
  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=10 
SourceImage = "*\\spoolsv.exe" CallTrace = "*\\Windows\\system32\\spool\\DRIVERS\\x64\\*" TargetImage IN ("*\\rundll32.exe", "*\\spoolsv.exe") GrantedAccess = 0x1fffff 
| stats count min(_time) AS firstTime max(_time) AS lastTime BY Computer SourceImage TargetImage GrantedAccess CallTrace  EventCode

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=10 Search for a process opening another process.
SourceImage = "*\\spoolsv.exe" Search for the spoolsv.exe source image.

CallTrace = "*\\Windows\\system32\\spool\\DRIVERS\\x64\\*" 
TargetImage IN ("*\\rundll32.exe", "*\\spoolsv.exe") GrantedAccess = 0x1fffff

Search for CallTrace = AND Target image matches either one OR the other strings IN between the (), AND GrantedAccess = 0x1fffff

| stats  count min(_time) AS firstTime max(_time) AS lastTime BY Computer SourceImage TargetImage GrantedAccess CallTrace  EventCode Return the first and last times this process occurred and rename those fields as shown. Then, sort first by Computer and then by rest of the fields shown.

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.