HTTP Suspicious Tool User Agent

Name:HTTP Suspicious Tool User Agent
id:1ca76190-4997-4d19-b5bc-9e220b70c7d3
version:2
date:2025-10-09
author:Raven Tait, Splunk
status:deprecated
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_suspicious_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:'$info_max_time$'
analytic_story:['HTTP Request Smuggling']

asset_type:Network

mitre_attack_id:['T1071.001']

product:None

category:None

security_domain:network

tags:
  analytic_story:
    - 'HTTP Request Smuggling'
  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
manual_test:None