How to obtain information about a specific header in headers

[Airboi]

Current behavior

such like check if jwt token veified,

base.request.headers[potential_header] is Unexpected，can you help me?

metadata:
  language: v1-beta
  name: "JWT Token Signature Validation"
  description: "This BCheck checks if the server verifies the signature of JWT tokens in requests."
  author: "Your Name"
  tags: "JWT", "Security", "Authentication"

run for each:
  potential_header = "Jwt-Token"

given header then
  if "X-Jwt-Token" in {base.request.headers} then
    define:
      jwt_token = {base.request.headers[potential_header]}
      unsigned_token = {jwt_token.split('.')[0] + '.' + jwt_token.split('.')[1] + '.'}

    send request called check_unsigned:
      method: {base.request.method}
      path: {base.request.path}
      headers:
        {potential_header}: {unsigned_token}
      body: {base.request.body}

    if {check_unsigned.response.status_code} is "200" then
      report issue:
        severity: high
        confidence: certain
        detail: "The server does not verify the signature of the JWT token, making it vulnerable to forgery attacks."
        remediation: "Ensure the server validates the signature of JWT tokens before processing the request."
    end if
  end if

[Hannah-PortSwigger]

Hi

You cannot use define within the given ... then block. It must be used before the given ... then block.

To clarify, you wish to extract the value of a specific header from the base response, then use that in an outgoing request as your scan check?

[Airboi]

Yes, I want to extract the JWT token from the base request headers, modify it and request the modified data packet again, check the response to determine if there is a vulnerability with the JWT signature not checked