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.
- Type: TTP
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2021-07-01
- Author: Mauricio Velazco, Michael Haag, Splunk
- ID: 347fd388-da87-11eb-836d-acde48001122
|T1547.012||Print Processors||Persistence, Privilege Escalation|
|T1547||Boot or Logon Autostart Execution||Persistence, Privilege Escalation|
`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`
Associated Analytic Story
How To Implement
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.
Kill Chain Phase
Known False Positives
Limited false positives. Filter as needed.
|72.0||80||90||$process_name$ has been identified writing dll's to $file_path$ on endpoint $dest$. This behavior is suspicious and related to PrintNightmare.|
|CVE-2021-34527||Windows Print Spooler Remote Code Execution Vulnerability||9.0|
source | version: 1