Spoolsv Writing a DLL
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.
- Type: TTP
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2021-07-01
- Author: Mauricio Velazco, Michael Haag, Splunk
- ID: d5bf5cf2-da71-11eb-92c2-acde48001122
Annotations
ATT&CK
Kill Chain Phase
- Installation
- Exploitation
NIST
- DE.CM
CIS20
- CIS 10
CVE
ID | Summary | CVSS |
---|---|---|
CVE-2021-34527 | Windows Print Spooler Remote Code Execution Vulnerability | 9.0 |
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| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.process_name=spoolsv.exe by _time Processes.process_id Processes.process_name Processes.dest
| `drop_dm_object_name(Processes)`
| join process_guid, _time [
| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_path="*\\spool\\drivers\\x64\\*" Filesystem.file_name="*.dll" by _time Filesystem.dest Filesystem.file_create_time Filesystem.file_name Filesystem.file_path
| `drop_dm_object_name(Filesystem)`
| fields _time dest file_create_time file_name file_path process_name process_path process]
| dedup file_create_time
| table dest file_create_time, file_name, file_path, process_name
| `spoolsv_writing_a_dll_filter`
Macros
The SPL above uses the following Macros:
spoolsv_writing_a_dll_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Required fields
List of fields required to use this analytic.
- _time
- Filesystem.dest
- Filesystem.file_create_time
- Filesystem.file_name
- Filesystem.file_path
- Processes.process_name
- Processes.process_id
- Processes.process_name
- Processes.dest
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 and Filesystem
node.
Known False Positives
Unknown.
Associated Analytic Story
RBA
Risk Score | Impact | Confidence | Message |
---|---|---|---|
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. |
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
Reference
- https://www.truesec.com/hub/blog/fix-for-printnightmare-cve-2021-1675-exploit-to-keep-your-print-servers-running-while-a-patch-is-not-available
- https://www.truesec.com/hub/blog/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
source | version: 1