| ID | Technique | Tactic |
|---|---|---|
| T1485 | Data Destruction | Impact |
Detection: Common Ransomware Extensions
Description
The following analytic detects modifications to files with extensions commonly associated with ransomware. It leverages the Endpoint.Filesystem data model to identify changes in file extensions that match known ransomware patterns. This activity is significant because it suggests an attacker is attempting to encrypt or alter files, potentially leading to severe data loss and operational disruption. If confirmed malicious, this activity could result in the encryption of critical data, rendering it inaccessible and causing significant damage to the organization's data integrity and availability.
Search
1
2| tstats `security_content_summariesonly`
3 min(_time) as firstTime
4 max(_time) as lastTime
5 count latest(Filesystem.user) as user
6 values(Filesystem.file_path) as file_path
7 from datamodel=Endpoint.Filesystem
8 where NOT Filesystem.file_name IN (
9 "*.bat",
10 "*.cmd",
11 "*.com",
12 "*.cpl",
13 "*.dll",
14 "*.doc",
15 "*.docx",
16 "*.exe",
17 "*.gif",
18 "*.jar",
19 "*.jpeg",
20 "*.jpg",
21 "*.js",
22 "*.lnk",
23 "*.pif",
24 "*.png",
25 "*.ppt",
26 "*.pptx",
27 "*.ps1",
28 "*.psm1",
29 "*.scr",
30 "*.sys",
31 "*.txt",
32 "*.vbs",
33 "*.wsf",
34 "*.xls",
35 "*.xlsx"
36 )
37 by Filesystem.action Filesystem.dest
38 Filesystem.file_access_time Filesystem.file_create_time
39 Filesystem.file_hash Filesystem.file_modify_time
40 Filesystem.file_name Filesystem.file_path
41 Filesystem.file_acl Filesystem.file_size
42 Filesystem.process_guid Filesystem.process_id
43 Filesystem.user Filesystem.vendor_product
44
45| `drop_dm_object_name(Filesystem)`
46
47| rex field=file_name "(?<file_extension>(\.[^\.]+){1,2})$"
48
49| lookup update=true ransomware_extensions_lookup Extensions AS file_extension OUTPUT Extensions Name
50
51| search Name !=False
52
53| stats min(firstTime) as firstTime
54 max(lastTime) as lastTime
55 dc(file_path) as path_count
56 dc(file_name) as file_count
57 values(action) as action
58 values(file_access_time) as file_access_time
59 values(file_create_time) as file_create_time
60 values(file_hash) as file_hash
61 values(file_modify_time) as file_modify_time
62 values(file_acl) as file_acl
63 values(file_size) as file_size
64 values(file_path) as file_path
65 values(process_guid) as process_guid
66 values(process_id) as process_id
67 values(user) as user
68 values(vendor_product) as vendor_product
69 values(file_name) as file_name
70 values(file_extension) as file_extension
71 values(Name) as Name
72 by dest
73
74| where path_count > 1 OR file_count > 20
75
76| `common_ransomware_extensions_filter`
Data Source
| Name | Platform | Sourcetype | Source |
|---|---|---|---|
| Sysmon EventID 11 |  Windows |
'XmlWinEventLog' |
'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational' |
Macros Used
| Name | Value |
|---|---|
| security_content_summariesonly | summariesonly=summariesonly_config allow_old_summaries=oldsummaries_config fillnull_value=fillnull_config`` |
| common_ransomware_extensions_filter | search * |
common_ransomware_extensions_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
Actions on Objectives
DE.CM
CIS 10
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
You must be ingesting data that records the filesystem activity from your hosts to populate the Endpoint Filesystem data model node. To see the additional metadata, add the following fields, if not already present, please review the detailed documentation on how to create a new field within Mission Control Queue
Known False Positives
It is possible for a legitimate file with these extensions to be created. If this is a true ransomware attack, there will be a large number of files created with these extensions.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message:
The device $dest$ wrote $file_count$ files to $path_count$ path(s) with the $file_extension$ extension. This extension and behavior may indicate a $Name$ ransomware attack.
| Risk Object | Risk Object Type | Risk Score | Threat Objects |
|---|---|---|---|
| dest | system | 90 | No Threat Objects |
| user | user | 90 | No Threat Objects |
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: 17