splunk_escuAnomaly

HTTP Rapid POST with Mixed Status Codes

This detection identifies rapid-fire POST request attacks where an attacker sends more than 20 POST requests within a 5-second window, potentially attempting to exploit race conditions or overwhelm request handling. The pattern is particularly suspicious when responses vary in size or status codes, indicating successful exploitation attempts or probing for vulnerable endpoints.

MITRE ATT&CK

T1071.001 T1190 T1595

command-and-controlinitial-access

Detection Query

`nginx_access_logs` http_method="POST"
  | bin _time span=5s
  | rename dest_ip as dest
  | stats count, values(status) as status_codes, values(bytes_out) as bytes_out, values(uri_path) as uris
    BY _time, src_ip, dest,
       http_user_agent
  | where count>20
  | table _time, dest, src_ip, count, status_codes, bytes_out, http_user_agent
  | `http_rapid_post_with_mixed_status_codes_filter`

Author

Raven Tait, Splunk

Created

2026-03-10

Data Sources

Nginx Access

References

Tags

HTTP Request Smuggling

Raw Content

name: HTTP Rapid POST with Mixed Status Codes
id: c8c987d6-3a1a-4555-9a52-eea0741b6113
version: 3
date: '2026-03-10'
author: Raven Tait, Splunk
status: production
type: Anomaly
description: This detection identifies rapid-fire POST request attacks where an attacker sends more than 20 POST requests within a 5-second window, potentially attempting to exploit race conditions or overwhelm request handling. The pattern is particularly suspicious when responses vary in size or status codes, indicating successful exploitation attempts or probing for vulnerable endpoints.
data_source:
    - Nginx Access
search: |-
    `nginx_access_logs` http_method="POST"
      | bin _time span=5s
      | rename dest_ip as dest
      | stats count, values(status) as status_codes, values(bytes_out) as bytes_out, values(uri_path) as uris
        BY _time, src_ip, dest,
           http_user_agent
      | where count>20
      | table _time, dest, src_ip, count, status_codes, bytes_out, http_user_agent
      | `http_rapid_post_with_mixed_status_codes_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/
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: A potential attempt to perform request smuggling against a web server was detected. 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
    asset_type: Web Server
    mitre_attack_id:
        - T1071.001
        - T1190
        - T1595
    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_request_smuggling.log
          source: nginx:plus:kv
          sourcetype: nginx:plus:kv