OpenRefine is a free, open source tool for working with messy data. Prior to version 3.8.3, the `export-rows` command can be used in such a way that it reflects part of the request verbatim, with a Content-Type header also taken from the request. An attacker could lead a user to a malicious page that submits a form POST that contains embedded JavaScript code. This code would then be included in the response, along with an attacker-controlled `Content-Type` header, and so potentially executed in the victim's browser as if it was part of OpenRefine. The attacker-provided code can do anything the user can do, including deleting projects, retrieving database passwords, or executing arbitrary Jython or Closure expressions, if those extensions are also present. The attacker must know a valid project ID of a project that contains at least one row. Version 3.8.3 fixes the issue.