Detection: HTTP PUA User Agent

Updated Date: 2025-12-17 ID: 21af5447-734f-4549-956b-7a255cb2b032 Author: Raven Tait, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

This Splunk query analyzes web logs to identify and categorize user agents, detecting various types of unwanted applications. This activity can signify possible compromised hosts on the network.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Web where Web.http_user_agent != null by Web.http_user_agent Web.http_method, Web.url, Web.url_length Web.src, Web.dest 
3| `drop_dm_object_name("Web")` 
4| lookup pua_user_agents pua_user_agent AS http_user_agent OUTPUT tool 
5| where isnotnull(tool) 
6| stats count min(firstTime) as first_seen max(lastTime) as last_seen by tool url http_user_agent src dest 
7| `security_content_ctime(first_seen)` 
8| `security_content_ctime(last_seen)` 
9| `http_pua_user_agent_filter`

Data Source

Name	Platform	Sourcetype	Source
Suricata	Other	`'suricata'`	`'suricata'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
http_pua_user_agent_filter	`search *`

http_pua_user_agent_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
T1071.001	Web Protocols	Command And Control

Command and Control

DE.AE

CIS 13

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 Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To successfully implement this search, you need to be ingesting web or proxy logs, or ensure it is being filled by a proxy like device, into the Web Datamodel. For additional filtering, allow list private IP space or restrict by known good.

Known False Positives

Noise and false positive can be seen if these programs are allowed to be used within corporate network. In this case, a filter is needed.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

A known user agent ($http_user_agent$) associated with unusual programs was performing a request from $src$.

Risk Object	Risk Object Type	Risk Score	Threat Objects
src	system	32	http_user_agent

References

https://github.com/mthcht/awesome-lists/blob/main/Lists/suspicious_http_user_agents_list.csv

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`suricata`	`suricata`
Integration	✅ Passing	Dataset	`suricata`	`suricata`

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: 1