Windows Spooler Service Suspicious Binary Load

Status: test
Severity: informational
Log source: category image_load, product windows
Author: FPT.EagleEye, Thomas Patzke (improvements)
Source: github.com/SigmaHQ/sigma

Detect DLL Load from Spooler Service backup folder. This behavior has been observed during the exploitation of the Print Spooler Vulnerability CVE-2021-1675 and CVE-2021-34527 (PrinterNightmare).

Known false positives

Loading of legitimate driver

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1574` Hijack Execution Flow
Stealth	`T1574` Hijack Execution Flow

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 7: Image loaded

Rule body

title: Windows Spooler Service Suspicious Binary Load
id: 02fb90de-c321-4e63-a6b9-25f4b03dfd14
status: test
description: |
    Detect DLL Load from Spooler Service backup folder. This behavior has been observed during the exploitation of the Print Spooler Vulnerability CVE-2021-1675 and CVE-2021-34527 (PrinterNightmare).
references:
    - https://web.archive.org/web/20210629055600/https://github.com/hhlxf/PrintNightmare/
    - https://github.com/ly4k/SpoolFool
author: FPT.EagleEye, Thomas Patzke (improvements)
date: 2021-06-29
modified: 2022-06-02
tags:
    - attack.persistence
    - attack.privilege-escalation
    - attack.execution
    - attack.stealth
    - attack.t1574
    - cve.2021-1675
    - cve.2021-34527
    - detection.emerging-threats
logsource:
    category: image_load
    product: windows
detection:
    selection:
        Image|endswith: '\spoolsv.exe'
        ImageLoaded|contains:
            - '\Windows\System32\spool\drivers\x64\3\'
            - '\Windows\System32\spool\drivers\x64\4\'
        ImageLoaded|endswith: '.dll'
    condition: selection
falsepositives:
    - Loading of legitimate driver
level: informational

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    Image|endswith: '\spoolsv.exe'
    ImageLoaded|contains:
        - '\Windows\System32\spool\drivers\x64\3\'
        - '\Windows\System32\spool\drivers\x64\4\'
    ImageLoaded|endswith: '.dll'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Image`	ends_with	`\spoolsv.exe` corpus 3 (sigma 3)	`field:"Image" kind:ends_with value:"\spoolsv.exe"`
`ImageLoaded`	ends_with	`.dll` corpus 6 (sigma 3, splunk 3)	`field:"ImageLoaded" kind:ends_with value:".dll"`
`ImageLoaded`	match	`\Windows\System32\spool\drivers\x64\3\` `\Windows\System32\spool\drivers\x64\4\`	`field:"ImageLoaded" kind:match`