Detection rules › Splunk
Email files written outside of the Outlook directory
The following analytic detects email files (.pst or .ost) being created outside the standard Outlook directories. It leverages the Endpoint.Filesystem data model to identify file creation events and filters for email files not located in "C:\Users*\My Documents\Outlook Files*" or "C:\Users*\AppData\Local\Microsoft\Outlook*". This activity is significant as it may indicate data exfiltration or unauthorized access to email data. If confirmed malicious, an attacker could potentially access sensitive email content, leading to data breaches or further exploitation within the network.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Collection | T1114.001 Email Collection: Local Email Collection |
Event coverage
| Provider | Event ID | Title |
|---|---|---|
| Sysmon | 11 | FileCreate |
Stages and Predicates
Stage 1: tstats
tstats WHERE (Filesystem.file_name="*.ost" OR Filesystem.file_name="*.pst") Filesystem.file_path!="C:\Users\*\AppData\Local\Microsoft\Outlook*" Filesystem.file_path!="C:\Users\*\My Documents\Outlook Files\*" 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
Stage 2: search
search
Stage 3: search
search
Stage 4: search
search
Stage 5: search
search `macro`
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
| Field | Kind | Values |
|---|---|---|
Filesystem.file_name | eq |
|
Filesystem.file_path | ne |
|