On: $ cat ~/myfile | curl -X PUT --upload-file “-” htt...

[rybosome]

If you can get that script to run on a user's machine, they're hosed whether or not this service exists. Curl or mail to an endpoint in the attacker's control would be equally effective.

[dzhiurgis → rybosome]

Sorry, I did not intend to discount this service in any way. More like showing a practical use.