HTTP Scripting Tool User Agent

name: HTTP Scripting Tool User Agent
id: 04430b4e-5ca8-4e88-98b5-d6bcf54f8393
version: 3
date: '2026-03-10'
author: Raven Tait, Splunk
status: production
type: Anomaly
description: This Splunk query analyzes web access logs to identify and categorize non-browser user agents, detecting various types of security tools, scripting languages, automation frameworks, and suspicious patterns. This activity can signify malicious actors attempting to interact with web endpoints in non-standard ways.
data_source:
    - Nginx Access
search: |-
    `nginx_access_logs`
      | eval http_user_agent = lower(http_user_agent)
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `drop_dm_object_name(Web)`
      | lookup scripting_tools_user_agents tool_user_agent AS http_user_agent OUTPUT tool
      | where isnotnull(tool)
      | rename dest_ip as dest
      | stats count min(firstTime) as first_seen max(lastTime) as last_seen values(tool) as tool
        BY http_user_agent dest src_ip
           status
      | `http_scripting_tool_user_agent_filter`
how_to_implement: This analytic necessitates the collection of web data, which can be achieved through Splunk Stream or by utilizing the Splunk Add-on for Apache Web Server. No additional configuration is required for this analytic.
known_false_positives: False positives may be present if the activity is part of diagnostics or testing. Filter as needed.
references:
    - https://portswigger.net/web-security/request-smuggling#what-is-http-request-smuggling
    - https://portswigger.net/research/http1-must-die
    - https://www.vaadata.com/blog/what-is-http-request-smuggling-exploitations-and-security-best-practices/
    - https://www.securityweek.com/new-http-request-smuggling-attacks-impacted-cdns-major-orgs-millions-of-websites/
    - https://github.com/SigmaHQ/sigma/blob/master/rules/web/proxy_generic/proxy_ua_hacktool.yml
    - https://help.aikido.dev/zen-firewall/miscellaneous/bot-protection-details
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") starthoursago=168  | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: Known scripting tool was used against a web request. The source IP is $src_ip$ and the destination is $dest$.
    risk_objects:
        - field: dest
          type: system
          score: 20
    threat_objects:
        - field: src_ip
          type: ip_address
tags:
    analytic_story:
        - HTTP Request Smuggling
        - Suspicious User Agents
    asset_type: Network
    mitre_attack_id:
        - T1071.001
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: network
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1190/request_smuggling/nginx_scripting_tools.log
          source: nginx:plus:kv
          sourcetype: nginx:plus:kv