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Spoolsv Writing A DLL - Sysmon

Description

The following analytic identifies a .dll being written by 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 write a .dll. Current POC code used will write the suspicious DLL to disk within a path of \spool\drivers\x64\. During triage, isolate the endpoint and review for source of exploitation. Capture any additional file modification events.

Help
Spoolsv Writing A DLL - Sysmon Help To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA. Tune and filter known instances where renamed rundll32.exe may be used.

Help

Spoolsv Writing A DLL - Sysmon Help

To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA. Tune and filter known instances where renamed rundll32.exe may be used.

Search
`sysmon` EventID=11 process_name=spoolsv.exe file_path="\\spool\\drivers\\x64\\" file_name=*.dll \| stats count min(_time) as firstTime max(_time) as lastTime by dest, UserID, process_name, file_path, file_name, TargetFilename, process_id \| `security_content_ctime(firstTime)` \| `security_content_ctime(lastTime)` \| `spoolsv_writing_a_dll___sysmon_filter` Open in Search

Search

`sysmon` EventID=11 process_name=spoolsv.exe file_path="*\\spool\\drivers\\x64\\*" file_name=*.dll | stats count min(_time) as firstTime max(_time) as lastTime by dest, UserID, process_name, file_path, file_name, TargetFilename, process_id | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `spoolsv_writing_a_dll___sysmon_filter`

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