Detection: Linux Usermod Root UID Set

Description

The following analytic detects the use of usermod to set a user's UID to 0. This functionally sets the user as a root user with full permissions. This approach can be used to bypass regular privilege escalation mechanisms, giving the attacker full control over the system while appearing as a regular user in most monitoring tools.

Search

 1
 2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
 3as lastTime FROM datamodel=Endpoint.Processes
 4WHERE Processes.process_name="usermod"
 5  AND (Processes.process IN ("* -u 0 *", "* -u 0") OR Processes.process="*--uid 0*")
 6BY Processes.action Processes.dest Processes.original_file_name
 7   Processes.parent_process Processes.parent_process_exec Processes.parent_process_guid
 8   Processes.parent_process_id Processes.parent_process_name Processes.parent_process_path
 9   Processes.process Processes.process_current_directory Processes.process_exec
10   Processes.process_guid Processes.process_hash Processes.process_id
11   Processes.process_integrity_level Processes.process_name Processes.process_path
12   Processes.user Processes.user_id Processes.vendor_product
13
14| `drop_dm_object_name(Processes)`
15
16| `security_content_ctime(firstTime)`
17
18| `security_content_ctime(lastTime)`
19
20| `linux_usermod_root_uid_set_filter`

Data Source

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

Macros Used

Annotations

Default Configuration

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

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

Setting a user's UID to 0 is extremely rare in legitimate administration — there is almost no valid operational reason to create a second root-equivalent account this way. False positives are expected to be very low. Verify any alert against change management records before dismissing.

Associated Analytic Story

• Linux Post-Exploitation

• Linux Privilege Escalation

• Linux Persistence Techniques

Finding

Intermediate Findings

Threat Objects

References

• https://github.com/Aegrah/PANIX

Detection Testing

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: 1