Detection: Splunk unnecessary file extensions allowed by lookup table uploads

Date: 2024-05-28 ID: b7d1293f-e78f-415e-b5f6-443df3480082 Author: Rod Soto, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies user activity related to uploading lookup tables with unnecessary filename extensions in Splunk Enterprise versions below 8.1.13, 8.2.10, and 9.0.4. It detects this activity by monitoring HTTP methods (POST, DELETE) and specific URI paths in the internal splunkd_access logs. This behavior is significant because it can indicate attempts to upload potentially malicious files disguised as lookup tables. If confirmed malicious, this activity could allow an attacker to execute unauthorized code or manipulate data within the Splunk environment, leading to potential data breaches or system compromise.

1`splunkda` method IN ("POST", "DELETE") uri_path=/servicesNS/*/ui/views/* 
2| eval activity = case( method=="POST" AND like( uri_path , "%/acl" ) , "Permissions Update", method=="POST" AND NOT like( uri_path , "%/acl" ) , "Edited" , method=="DELETE" , "Deleted" ) 
3| rex field=uri_path "(?<user_and_app>.*?)\/ui\/views/(?<dashboard_encoded>.*)" 
4| eval dashboard = urldecode( dashboard_encoded ) 
5| table _time, uri_path, user, dashboard, activity, uri_path 
6| `splunk_unnecessary_file_extensions_allowed_by_lookup_table_uploads_filter`

Data Source

Name Platform Sourcetype Source Supported App
Splunk Splunk icon Splunk 'splunkd_ui_access' 'splunkd_ui_access.log' N/A

Macros Used

Name Value
splunkda index=_internal sourcetype=splunkd_access
splunk_unnecessary_file_extensions_allowed_by_lookup_table_uploads_filter search *
splunk_unnecessary_file_extensions_allowed_by_lookup_table_uploads_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
ID Technique Tactic
T1189 Drive-by Compromise Initial Access
KillChainPhase.DELIVERY
NistCategory.DE_CM
Cis18Value.CIS_10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Enabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Risk Based Alerting True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

Requires access to internal splunkd_access.

Known False Positives

This is a hunting search, the search provides information on upload, edit, and delete activity on Lookup Tables. Manual investigation is necessary after executing search. This search will produce false positives as payload cannot be directly discerned.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
Potential lookup template injection attempt from $user$ on lookup table at path $uri_path$ 25 50 50
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset /opt/splunk/var/log/splunk/splunkd_access.log splunkd_access
Integration ✅ Passing Dataset /opt/splunk/var/log/splunk/splunkd_access.log splunkd_access

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: 2