Detection: Linux pkexec Privilege Escalation

Description

The following analytic detects the execution of pkexec without any command-line arguments. This behavior leverages data from Endpoint Detection and Response (EDR) agents, focusing on process telemetry. The significance lies in the fact that this pattern is associated with the exploitation of CVE-2021-4034 (PwnKit), a critical vulnerability in Polkit's pkexec component. If confirmed malicious, this activity could allow an attacker to gain full root privileges on the affected Linux system, leading to complete system compromise and potential unauthorized access to sensitive information.

1
2| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.process_name=pkexec by _time Processes.dest Processes.user Processes.process_id Processes.parent_process_name Processes.process_name Processes.process Processes.process_path 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| regex process="(^.{1}$)" 
7| `linux_pkexec_privilege_escalation_filter`

Data Source

Name Platform Sourcetype Source
Sysmon for Linux EventID 1 Linux icon Linux 'sysmon:linux' 'Syslog:Linux-Sysmon/Operational'

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
linux_pkexec_privilege_escalation_filter search *
linux_pkexec_privilege_escalation_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
Volt Typhoon
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

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

False positives may be present, filter as needed.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest$ by user $user$ related to a local privilege escalation in polkit pkexec. 56 80 70
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 Syslog:Linux-Sysmon/Operational sysmon:linux
Integration ✅ Passing Dataset Syslog:Linux-Sysmon/Operational sysmon:linux

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: 4