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26. errors: malformed request header

Last updated on Aug 05, 2025

MALFORMED_REQUEST_HEADER

The MALFORMED_REQUEST_HEADER error occurs when a request contains an improperly formatted or invalid header.

Table of Contents

The MALFORMED_REQUEST_HEADER error

The MALFORMED_REQUEST_HEADER error signifies that a request made to the server includes a header that is incorrectly formatted or contains invalid data. This could be due to syntax errors, incorrect header field names, or incompatible header values.

400 MALFORMED_REQUEST_HEADER Bad Request

Troubleshoot

  1. Inspect request headers : Review the headers in your request. Ensure that they are correctly formatted and adhere to the HTTP standard.
  2. Validate UTF-8 encoding : Confirm that all request headers, especially cookie values, are valid UTF-8 strings. Non-UTF-8 characters in headers, particularly in the cookie header, often cause this error
  3. Examine Serverless Function behavior : Since this error is specific to Serverless Functions, verify the functionality and responses of your Serverless Functions. Ensure they are correctly handling request headers and not contributing to malformed responses