Detection: Spoolsv Suspicious Process Access

Updated Date: 2024-08-14 ID: 799b606e-da81-11eb-93f8-acde48001122 Author: Mauricio Velazco, Michael Haag, Teoderick Contreras, Splunk Type: TTP Product: Splunk Enterprise Security

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.

Search

1`sysmon` EventCode=10 SourceImage = "*\\spoolsv.exe" CallTrace = "*\\Windows\\system32\\spool\\DRIVERS\\x64\\*" TargetImage IN ("*\\rundll32.exe", "*\\spoolsv.exe") GrantedAccess = 0x1fffff 
2| stats  count min(_time) as firstTime max(_time) as lastTime by dest SourceImage TargetImage GrantedAccess CallTrace  EventCode ProcessID
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `spoolsv_suspicious_process_access_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Sysmon EventID 10	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`	N/A

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
spoolsv_suspicious_process_access_filter	`search *`

spoolsv_suspicious_process_access_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1068	Exploitation for Privilege Escalation	Privilege Escalation

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

APT28

APT29

APT32

APT33

BITTER

Cobalt Group

FIN6

FIN8

LAPSUS$

MoustachedBouncer

PLATINUM

Scattered Spider

Threat Group-3390

Tonto Team

Turla

Whitefly

ZIRCONIUM

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

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.

Associated Analytic Story

PrintNightmare CVE-2021-34527

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
$SourceImage$ was GrantedAccess open access to $TargetImage$ on endpoint $dest$. This behavior is suspicious and related to PrintNightmare.	72	80	90

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`xmlwineventlog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`xmlwineventlog`

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: GitHub | Version: 3