Windows Change Default File Association For No File Ext
This analytic is developed to detect suspicious process commandline to change or set the default file association of a file without file extension with notepad.exe. This technique was seen in some APT and ransomware Prestige where it set/modify the default process to run file association, like .txt to notepad.exe.
- Type: TTP
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2022-11-30
- Author: Teoderick Contreras, Splunk
- ID: dbdf52ad-d6a1-4b68-975f-0a10939d8e38
Kill Chain Phase
- CIS 10
1 2 3 4 5 6 7 8 9 | tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_reg` AND Processes.process="* add *" AND Processes.process="* HKCR\\*" AND Processes.process="*\\shell\\open\\command*" AND Processes.process= *Notepad.exe* by Processes.process_name Processes.original_file_name Processes.process Processes.process_id Processes.process_guid Processes.parent_process_name Processes.parent_process Processes.parent_process_guid Processes.dest Processes.user | `drop_dm_object_name(Processes)` | rex field=process "Notepad\.exe (?<file_name_association>.*$)" | rex field=file_name_association "\.(?<extension>[^\.]*$)" | where isnull(extension) and isnotnull(file_name_association) | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `windows_change_default_file_association_for_no_file_ext_filter`
The SPL above uses the following Macros:
windows_change_default_file_association_for_no_file_ext_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
List of fields required to use this analytic.
How To Implement
To successfully implement this search, you must be ingesting data that records registry activity from your hosts to populate the endpoint data model in the registry node. This is typically populated via endpoint detection-and-response product, such as Carbon Black or endpoint data sources, such as Sysmon. The data used for this search is typically generated via logs that report reads and writes to the registry.
Known False Positives
Associated Analytic Story
|80.0||80||100||process with commandline $process$ set or change the file association of a file with no file extension in $dest$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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