Security News > 2021 > May > Google Researchers Discover A New Variant of Rowhammer Attack

A team of security researchers from Google has demonstrated yet another variant of the Rowhammer vulnerability that targets increasingly smaller DRAM chips to bypass all current mitigations, making it a persistent threat to chip security.

Dubbed "Half-Double," the new hammering technique hinges on the weak coupling between two memory rows that are not immediately adjacent to each other but one row removed in an attempt to tamper with data stored in memory and attack a system.

Discovered in 2014, Rowhammer refers to a class of DRAM vulnerabilities whereby repeated accesses to a memory row can induce an electrical disturbance big enough to flip bits stored in an adjacent row, thereby allowing untrusted code to escape its sandbox and take over control of the system.

"[The attack] works because DRAM cells have been getting smaller and closer together," Google Project Zero researchers elaborated in 2015.

The imperfect protections meant TRR defenses in DDR4 cards could be circumvented to stage new variants of Rowhammer attacks such as TRRespass and SMASH. The distance-two assisted Rowhammer - aka Half-Double - now joins that list.

"Given three consecutive rows A, B, and C, we were able to attack C by directing a very large number of accesses to A, along with just a handful to B," the researchers explained.

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