Modern DRAM devices (PC-DDR4, LPDDR4X) are affected by a vulnerability in their internal Target Row Refresh (TRR) mitigation against Rowhammer attacks. Novel non-uniform Rowhammer access patterns, consisting of aggressors with different frequencies, phases, and amplitudes allow triggering bit flips on affected memory modules using our Blacksmith fuzzer. The patterns generated by Blacksmith were able to trigger bitflips on all 40 PC-DDR4 DRAM devices in our test pool, which cover the three major DRAM manufacturers: Samsung, SK Hynix, and Micron. This means that, even when chips advertised as Rowhammer-free are used, attackers may still be able to exploit Rowhammer. For example, this enables privilege-escalation attacks against the kernel or binaries such as the sudo binary, and also triggering bit flips in RSA-2048 keys (e.g., SSH keys) to gain cross-tenant virtual-machine access. We can confirm that DRAM devices acquired in July 2020 with DRAM chips from all three major DRAM vendors (Samsung, SK Hynix, Micron) are affected by this vulnerability. For more details, please refer to our publication.

Modern DRAM chips (DDR4 and LPDDR4 after 2015) are affected by a vulnerability in deployment of internal mitigations against RowHammer attacks known as Target Row Refresh (TRR), aka the TRRespass issue. To exploit this vulnerability, the attacker needs to create certain access patterns to trigger bit flips on affected memory modules, aka a Many-sided RowHammer attack. This means that, even when chips advertised as RowHammer-free are used, attackers may still be able to conduct privilege-escalation attacks against the kernel, conduct privilege-escalation attacks against the Sudo binary, and achieve cross-tenant virtual-machine access by corrupting RSA keys. The issue affects chips produced by SK Hynix, Micron, and Samsung. NOTE: tracking DRAM supply-chain issues is not straightforward because a single product model from a single vendor may use DRAM chips from different manufacturers.