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Race Conditions are another class of bugs not easily automated via traditional tooling. Burp Suite introduced a Gate mechanism to Turbo Intruder where all the bytes for all the requests are sent expect the last one at once which is only sent together for all requests synchronizing the send event. We have implemented Gate mechanism in nuclei engine and allow them run via templates which makes the testing for this specific bug class simple and portable. To enable race condition check within template, race attribute can be set to true and race_count defines the number of simultaneous request you want to initiate. Below is an example template where the same request is repeated for 10 times using the gate logic. 
id: race-condition-testing

info:
  name: Race condition testing
  author: pdteam
  severity: info

http:
  - raw:
      - |
        POST /coupons HTTP/1.1
        Host: {{Hostname}}

        promo_code=20OFF        

    race: true
    race_count: 10

    matchers:
      - type: status
        part: header
        status:
          - 200
You can simply replace the POST request with any suspected vulnerable request and change the race_count as per your need, and it’s ready to run. 
nuclei -t race.yaml -target https://api.target.com
Multi request race condition testing For the scenario when multiple requests needs to be sent in order to exploit the race condition, we can make use of threads. 
    threads: 5
    race: true
threads is a total number of request you wanted make with the template to perform race condition testing. Below is an example template where multiple (5) unique request will be sent at the same time using the gate logic. 
id: multi-request-race

info:
  name: Race condition testing with multiple requests
  author: pd-team
  severity: info

http:
  - raw:  
      - |
        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

        id=1
        
      - |
        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

        id=2

      - |
        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

        id=3

      - |
        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

        id=4

      - |
        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

        id=5

    threads: 5
    race: true
More complete examples are provided here
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