I'm playing around with a self-xss bug that I believe I can escalate with a CSRF attack. However, the exploit relies on sending two identical Content-Length
headers in a single POST request.
Essentially, I'm looking for a piece of Javascript code that will make the visitor's browser issue a request that looks like this:
POST /authenticate[xss payload]
Host: target.net
Content-Length: 4
Content-Length: 4
whatever=whatever
It doesn't matter if the Content-Length is correct or not - there just has to be two identical Content-Length headers.
Sorry if the answer to this is trivial, I hope you can cut an infosec n00b some slack.