Who reported this?

Plundervolt was first reported on June 7, 2019 by a group of international researchers:

Before that, Navjivan Pal looked at the potential of using undervolting for faulting (non-SGX) computations within his final year project at the University of Birmingham under supervision of David Oswald.

We were also informed by Intel that other researchers reported a similar issue after our initial disclosure to Intel on 7 June 2019. The two other research teams who independently reported this issue are VoltJockey and V0LTpwn. Intel has confirmed that we were the first group to report this issue.