Another Rowhammer attack has been detected, and Nvidia workstation GPUs are firmly in the firing line

A new Rowhammer attack, dubbed GPUThor, has emerged with the capability to bypass error correction on Nvidia workstation GPUs, potentially leading to a root shell on the host system. This attack targets four Ampere workstation cards equipped with GDDR6 memory, including the RTX A4000, A4500, A5000, and A6000 models. Researchers from the University of Toronto disclosed the technique, which exploits non-uniform hammering to deliver significantly higher bit flipping intensity compared to previous attacks.

By disabling Nvidia's error correction capabilities through ECC, the researchers were able to achieve 6.6 times the hammering intensity of prior attacks, resulting in up to 377,000 bit flips per gigabyte. This poses a serious threat, as GPU Rowhammer is now on par with CPU Rowhammer attacks. When ECC is enabled, GPUThor still forces one GPU reset every two hours, causing all running processes to terminate and flagging the GPU as needing replacement within a day.

The researchers have notified Nvidia, as well as Google, Microsoft, and AWS about the vulnerability, and a code release is expected in November, although no official patch has been issued yet.