FPGAs are proving useful and attractive for many applications, thanks to their hardware reconfigurability, low power, and high-degree of parallelism. As a result, modern embedded systems are often based on systems-on-chip (SoCs), where CPUs and FPGAs share the same die. In this paper, we demonstrate the first undervolting attack in which the FPGA acts as an aggressor while the CPU, residing on the same SoC, is the victim. We show that an adversary can use the FPGA fabric to create a significant supply voltage drop which, in turn, faults the software computation performed by the CPU. Additionally, we show that an attacker can, with an even higher success rate, execute a denial-of-service attack, without any modification of the underlying hardware or the power distribution network. Our work exposes a new electrical-level attack surface, created by tight integration of CPUs and FPGAs in m