Researchers Show DRAM “Rowhammer” Bug Can Be Exploited Remotely

A team of researchers from Austria and France have demonstrated what they claim to be the first remote software-induced hardware fault attack. They have found a way to exploit the “Rowhammer” vulnerability remotely by using JavaScript.

Google researchers demonstrated in March that a bug affecting some dynamic random-access memory (DRAM) chips can be exploited to gain kernel privileges on Linux and other systems.

The vulnerability exists because the memory cells in DRAM chips have been placed very close together to increase capacity and decreasing size. This makes it more difficult to prevent cells from electrically interacting with each other. Repeatedly accessing specific memory locations causes bit flips which, as Google researchers demonstrated, can be used for privilege escalation.

However, the exploits created by Google experts have been written in native code, they rely on special instructions, and they require physical access to the targeted machine.

Researchers have now demonstrated that such hardware fault attacks can be carried out remotely using JavaScript.

Rowhammer.js does not require the execution of native code or access to special instructions. And since it leverages JavaScript, the attack can be launched against a large number of users simultaneously from a malicious website.

While Rowhammer.js has been implemented in JavaScript on Firefox, the experts have pointed out that the technique they describe can be adapted to any architecture, runtime environment and programming language as long as an efficient stream of memory access instructions can be produced. They have also noted that their proof-of-concept (PoC) attack does not rely on any JavaScript or browser vulnerabilities.

“Rowhammer.js is possible because today’s JavaScript implementations are well optimized and achieve almost native code performance for our use case. JavaScript is strictly sandboxed and the language provides no possibility to retrieve virtual or physical addresses. However, the usage of large pages allows determining parts of the physical address,” reads the research paper published last week.

Researchers have demonstrated that a Rowhammer attack can be launched using JavaScript, but they have not developed a full root exploit. However, they believe malicious actors could adapt existing Rowhammer exploits to their attack technique in order to gain root privileges.

Some hardware manufacturers, including Apple, have already started releasing BIOS updates to mitigate Rowhammer attacks. However, since many users never update the BIOS, experts propose a different approach. They advise browser vendors to integrate Rowhammer protection mechanisms in their products.