Even a deposit works well (and doesn't have to be large). Someone who has actually found a serious bug in cURL will probably pay $2-5 dollars as a deposit to report (especially given the high probability of a payout).
I'd sooner click sponsor for the cURL project on github (something I already do for some OSS I use) than spend money to report a bug.
I’d love to have this for phone calls and sms as well. If you didn’t spam me, I’ll refund.