ID | Technique | Tactic |
---|---|---|
T1566 | Phishing | Initial Access |
T1566.001 | Spearphishing Attachment | Initial Access |
Detection: Detect Outlook exe writing a zip file
EXPERIMENTAL DETECTION
This detection status is set to experimental. The Splunk Threat Research team has not yet fully tested, simulated, or built comprehensive datasets for this detection. As such, this analytic is not officially supported. If you have any questions or concerns, please reach out to us at research@splunk.com.
Description
The following analytic identifies the execution of outlook.exe
writing a .zip
file to the disk. It leverages data from the Endpoint data model, specifically monitoring process and filesystem activities. This behavior is significant as it may indicate the use of Outlook to deliver malicious payloads or exfiltrate data via compressed files. If confirmed malicious, this activity could lead to unauthorized data access, data exfiltration, or the delivery of malware, potentially compromising the security of the affected system and network.
Search
1
2| tstats `security_content_summariesonly` min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Processes where Processes.process_name=outlook.exe by _time span=5m Processes.parent_process_id Processes.process_id Processes.dest Processes.process_name Processes.parent_process_name Processes.user
3| `drop_dm_object_name(Processes)`
4| `security_content_ctime(firstTime)`
5| `security_content_ctime(lastTime)`
6| rename process_id as malicious_id
7| rename parent_process_id as outlook_id
8| join malicious_id type=inner[
9| tstats `security_content_summariesonly` count values(Filesystem.file_path) as file_path values(Filesystem.file_name) as file_name FROM datamodel=Endpoint.Filesystem where (Filesystem.file_path=*.zip* OR Filesystem.file_name=*.lnk ) AND (Filesystem.file_path=C:\\Users* OR Filesystem.file_path=*Local\\Temp*) by _time span=5m Filesystem.process_id Filesystem.file_hash Filesystem.dest
10| `drop_dm_object_name(Filesystem)`
11| `security_content_ctime(firstTime)`
12| `security_content_ctime(lastTime)`
13| rename process_id as malicious_id
14| fields malicious_id outlook_id dest file_path file_name file_hash count file_id]
15| table firstTime lastTime user malicious_id outlook_id process_name parent_process_name file_name file_path
16| where file_name != ""
17| `detect_outlook_exe_writing_a_zip_file_filter`
Data Source
Name | Platform | Sourcetype | Source |
---|---|---|---|
Sysmon EventID 1 | Windows | 'xmlwineventlog' |
'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational' |
Sysmon EventID 11 | Windows | 'xmlwineventlog' |
'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational' |
Macros Used
Name | Value |
---|---|
security_content_ctime | convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$) |
detect_outlook_exe_writing_a_zip_file_filter | search * |
detect_outlook_exe_writing_a_zip_file_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
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 |
Implementation
You must be ingesting data that records filesystem and process activity from your hosts to populate the Endpoint data model. This is typically populated via endpoint detection-and-response product, such as Carbon Black, or endpoint data sources, such as Sysmon.
Known False Positives
It is not uncommon for outlook to write legitimate zip files to the disk.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message | Risk Score | Impact | Confidence |
---|---|---|---|
tbd | 25 | 50 | 50 |
Detection Testing
Test Type | Status | Dataset | Source | Sourcetype |
---|---|---|---|---|
Validation | Not Applicable | N/A | N/A | N/A |
Unit | ❌ Failing | N/A | N/A |
N/A |
Integration | ❌ Failing | N/A | N/A |
N/A |
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: 8