Detection: Windows File and Directory Enable ReadOnly Permissions

Description

The following analytic detects instances where file or folder permissions are modified to grant read-only access. Such changes are characterized by the presence of read-related permissions (e.g., R, REA, RA, RD) and the absence of write (W) or execute (E) permissions. Monitoring these events is crucial for tracking access control changes that could be intentional for restricting access or indicative of malicious behavior. Alerts generated by this detection help ensure that legitimate security measures are enforced while unauthorized changes are promptly investigated.

Search

 1
 2| tstats `security_content_summariesonly` min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name IN( "icacls.exe", "cacls.exe", "xcacls.exe") AND Processes.process IN ("*/grant*", "*/G*") AND Processes.process IN ("*SYSTEM*", "*admin*", "*S-1-1-0*", "*EVERYONE*") by Processes.parent_process_name Processes.parent_process Processes.process_name Processes.process Processes.process_guid Processes.dest Processes.user 
 3| `drop_dm_object_name(Processes)` 
 4| rex field=process ":\\((?<permission>[^)]+)\\)" 
 5| eval has_read_attribute=if(match(permission, "R"), "true", "false") 
 6| eval has_write_execute=if(match(permission, "(W
 7|GA
 8|X
 9|M
10|F
11|AD
12|DC
13|DE)"), "true", "false") 
14| where has_write_execute="false" and has_read_attribute = "true" 
15| `security_content_ctime(firstTime)` 
16| `security_content_ctime(lastTime)` 
17| `windows_file_and_directory_enable_readonly_permissions_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 1	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Windows Event Log Security 4688	Windows	'xmlwineventlog'	'XmlWinEventLog:Security'

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

Administrators or administrative scripts may use this application. Filter as needed.

Associated Analytic Story

• Crypto Stealer

Risk Based Analytics (RBA)

Risk Message:

A [$process_name$] was executed on [$dest$] attempting to change the access to a file or directory into readonly permissions.

References

• https://www.splunk.com/en_us/blog/security/-applocker-rules-as-defense-evasion-complete-analysis.html

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