Spoolsv Suspicious Process Access

Name:Spoolsv Suspicious Process Access
id:799b606e-da81-11eb-93f8-acde48001122
version:8
date:2025-03-27
author:Mauricio Velazco, Michael Haag, Teoderick Contreras, Splunk
status:production
type:TTP
Description:The following analytic detects suspicious process access by spoolsv.exe, potentially indicating exploitation of the PrintNightmare vulnerability (CVE-2021-34527). It leverages Sysmon EventCode 10 to identify when spoolsv.exe accesses critical system files or processes like rundll32.exe with elevated privileges. This activity is significant as it may signal an attempt to gain unauthorized privilege escalation on a vulnerable machine. If confirmed malicious, an attacker could achieve elevated privileges, leading to further system compromise, persistent access, or unauthorized control over the affected environment.
Data_source:

• -Sysmon EventID 10

search:`sysmon` 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 CallTrace EventID GrantedAccess Guid Opcode ProcessID SecurityID SourceImage SourceProcessGUID SourceProcessId TargetImage TargetProcessGUID TargetProcessId UserID dest granted_access parent_process_exec parent_process_guid parent_process_id parent_process_name parent_process_path process_exec process_guid process_id process_name process_path signature signature_id user_id vendor_product
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `spoolsv_suspicious_process_access_filter`

how_to_implement:To successfully implement this search, you need to be ingesting logs with process access event where SourceImage, TargetImage, GrantedAccess and CallTrace 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 of spoolsv.exe.
known_false_positives:Unknown. Filter as needed.
References:
  -https://github.com/cube0x0/impacket/commit/73b9466c17761384ece11e1028ec6689abad6818
  -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
drilldown_searches:
 name:'View the detection results for - "$dest$"'
 search:'%original_detection_search% | search dest = "$dest$"'
 earliest_offset:'$info_min_time$'
 latest_offset:'$info_max_time$'
 name:'View risk events for the last 7 days for - "$dest$"'
 search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") starthoursago=168 | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
 earliest_offset:'$info_min_time$'
 latest_offset:'$info_max_time$'
tags:
  analytic_story:
    - 'PrintNightmare CVE-2021-34527'
    - 'Black Basta Ransomware'
  asset_type:Endpoint
  cve:
    - 'CVE-2021-34527'
  mitre_attack_id:
    - 'T1068'
  product:
    - 'Splunk Enterprise'
    - 'Splunk Enterprise Security'
    - 'Splunk Cloud'
  security_domain:endpoint

tests:
 name:'True Positive Test'
 attack_data:
  data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1547.012/printnightmare/windows-sysmon.log
  source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
  sourcetype: XmlWinEventLog
manual_test:None