Burp Suite Turbo Intruder Protocol Error

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If you’re experiencing the problem with Burp Suite’s Turbo Intruder Extension that the server replies with error message Protocol Error, this blogpost may help you solve it.

Problem Description

When sending HTTP requests with Turbo Intruder in Burp Suite, I received the following error message from the server:

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HTTP/1.1 400 Bad Request
Content-Type: application/json; charset=utf-8
Connection: close
Content-Length: 16

"Protocol error"

This is rather strange, and I did not solve it even I tried the following methods:

  1. Make sure \r\n is used correctly in the HTTP GET or POST request
  2. Make sure the https protocol is used as expected (rather than http)
  3. Make sure everything is the same with the original HTTP request

Solution

After debugging (or thinking) for a while, I noticed that I’m using the HTTP/2 protocol to send the request, but the server responded with HTTP/1.1.

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POST /my-account/avatar HTTP/2
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HTTP/1.1 400 Bad Request

Thus, I changed the HTTP protocol version from HTTP/2 to HTTP/1.1 in the request header. Then the problem disappeared :-D

I think this may be caused by the fact that my Turbo Intruder was released in 2020 which is rather old in 2025. Why did I install such an old version of Turbo Intruder? That’s because the latest version is not compatible with my Burp Suite.

I hope this article is useful for you if you’re experiencing the same "Protocol error" problem. Cheers!