Detection: HTTP Possible Request Smuggling

Updated Date: 2025-10-06 ID: 97d85f98-9d15-41a0-8682-7030454875e7 Author: Raven Tait, Splunk Type: TTP Product: Splunk Enterprise Security

Description

HTTP request smuggling is a technique for interfering with the way a web site processes sequences of HTTP requests that are received from one or more users. Request smuggling vulnerabilities are often critical in nature, allowing an attacker to bypass security controls, gain unauthorized access to sensitive data, and directly compromise other application users. This detection identifies a common request smuggling technique of using both Content-Length and Transfer-Encoding headers to cause a parsing confusion between the frontend and backend.

Search

1`suricata` (http.request_headers{}.name="*Content-Length*" http.request_headers{}.name="*Transfer-Encoding*") OR (http.request_headers{}.name="*Content-Length*" http.request_headers{}.value="*Transfer-Encoding*") OR (http.request_headers{}.value="*Content-Length*" http.request_headers{}.name="*Transfer-Encoding*") OR (http.request_headers{}.name="*Content-Length*" http.request_headers{}.value="0") 
2| rename dest_ip as dest 
3| rex field=_raw "request_headers.:\[(?<headers>.*)\]" 
4| stats count min(_time) as firstTime max(_time) as lastTime by dest, dest_port, src_ip, http.url, http.http_method, http.http_user_agent, http.protocol, http.status, headers 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `http_possible_request_smuggling_filter`

Data Source

Name	Platform	Sourcetype	Source
Suricata	N/A	`'suricata'`	`'suricata'`

Macros Used

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

http_possible_request_smuggling_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.CM

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 Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

This detection requires the Web datamodel to be populated from a supported Technology Add-On like Suricata, Splunk for Apache, Splunk for Nginx, or Splunk for Palo Alto. Some of these will need to have all headers dumped to contain the necessary fields.

Known False Positives

False positives are not expected, however, monitor, filter, and tune as needed based on organization log sources.

Associated Analytic Story

HTTP Request Smuggling

Risk Based Analytics (RBA)

Risk Message:

Possible request smuggling against a web request was detected. The source IP is $src_ip$ and the destination is $dest$.

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	60	src_ip

References

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