| ID | Technique | Tactic |
|---|---|---|
| T1486 | Data Encrypted for Impact | Impact |
Detection: Samsam Test File Write
Description
The following analytic detects the creation of a file named "test.txt" within the Windows system directory, indicative of Samsam ransomware propagation. It leverages file-system activity data from the Endpoint data model, specifically monitoring file paths within the Windows System32 directory. This activity is significant as it aligns with known Samsam ransomware behavior, which uses such files for propagation and execution. If confirmed malicious, this could lead to ransomware deployment, resulting in data encryption, system disruption, and potential data loss. Immediate investigation and remediation are crucial to prevent further damage.
Search
1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime values(Filesystem.user) as user values(Filesystem.dest) as dest values(Filesystem.file_name) as file_name from datamodel=Endpoint.Filesystem where Filesystem.file_path=*\\windows\\system32\\test.txt by Filesystem.action Filesystem.dest Filesystem.file_access_time Filesystem.file_create_time Filesystem.file_hash Filesystem.file_modify_time Filesystem.file_name Filesystem.file_path Filesystem.file_acl Filesystem.file_size Filesystem.process_guid Filesystem.process_id Filesystem.user Filesystem.vendor_product
3| `drop_dm_object_name(Filesystem)`
4| `security_content_ctime(lastTime)`
5| `security_content_ctime(firstTime)`
6| `samsam_test_file_write_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`` |
| samsam_test_file_write_filter | search * |
samsam_test_file_write_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 Finding (Notable) | Yes |
| Rule Title | %name% |
| Rule Description | %description% |
| Notable Event Fields | user, dest |
| Creates Intermediate Finding (Risk Event) | Yes |
TTP detections generate a Finding (Notable) and may generate Intermediate Findings (Risk Events) for associated entities.
Implementation
You must be ingesting data that records the file-system activity from your hosts to populate the Endpoint file-system data-model node. If you are using Sysmon, you will need a Splunk Universal Forwarder on each endpoint from which you want to collect data.
Known False Positives
No false positives have been identified.
Associated Analytic Story
Finding
| Title | Entity Field | Entity Type | Risk Score |
|---|---|---|---|
| A samsam ransomware test file creation in $file_path$ in host $dest$ | user | user | 50 |
Intermediate Findings
| Message | Entity Field | Entity Type | Risk Score |
|---|---|---|---|
| A samsam ransomware test file creation in $file_path$ in host $dest$ | dest | system | 50 |
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: 9