One of the most basic premises of computer security is isolation: If you run somebody else's sketchy code as an untrusted process on your machine, you should restrict it to its own tightly sealed playpen. Otherwise, it might peer into other processes, or snoop around the computer as a whole. So when a security flaw in computers' most deep-seated hardware puts a crack in those walls, as one newly discovered vulnerability in millions of processors has done, it breaks some of the most fundamental protections computers promise—and sends practically the entire industry scrambling.

Earlier this week, security researchers took note of a series of changes Linux and Windows developers began rolling out in beta updates to address a critical security flaw: A bug in Intel chips allows low-privilege processes to access memory in the computer's kernel, the machine's most privileged inner sanctum. Theoretical attacks that exploit that bug, based on quirks in features Intel has implemented for faster processing, could allow malicious software to spy deeply into other processes and data on the target computer or smartphone. And on multi-user machines, like the servers run by Google Cloud Services or Amazon Web Services, they could even allow hackers to break out of one user's process, and instead snoop on other processes running on the same shared server.

On Wednesday evening, a large team of researchers at Google's Project Zero, universities including the Graz University of Technology, the University of Pennsylvania, the University of Adelaide in Australia, and security companies including Cyberus and Rambus together released the full details of two attacks based on that flaw, which they call Meltdown and Spectre.

"These hardware bugs allow programs to steal data which [is] currently processed on the computer," reads a description of the attacks on a website the researchers created. "While programs are typically not permitted to read data from other programs, a malicious program can exploit Meltdown and Spectre to get hold of secrets stored in the memory of other running programs."

Although both attacks are based on the same general principle, Meltdown allows malicious programs to gain access to higher-privileged parts of a computer's memory, while Spectre steals data from the memory of other applications running on a machine. And while the researchers say that Meltdown is limited to Intel chips, they say that they've verified Spectre attacks on AMD and ARM processors, as well.

Ben Gras, a security researcher with Vrije Universiteit Amsterdam who specializes in chip-level hardware security, says that the attacks represent a deep and serious security breach. "With these glitches, if there's any way an attacker can execute code on a machine, it can’t be contained anymore," he says. (Gras was clear that he hadn't participated in any research that unearthed or reproduced the vulnerability, but he has watched the revelations of Intel's vulnerability unfold in the security community.) "For any process that’s untrusted and isolated, that safety is gone now," Gras adds. "Every process can spy on every other process and access secrets in the operating system kernel."

Meltdown and Spectre

Prior to the official revelation of Meltdown and Spectre on Wednesday, Erik Bosman, a colleague of Gras in Vrije Universiteit Amsterdam's VUSEC security group, successfully reproduced one of the Intel attacks, which take advantage of a feature in chips known as "speculative execution." When modern Intel processors execute code and come to a point in an algorithm where instructions branch in two different directions, depending on input data—whether there's enough money in an account to process a transaction, for instance—they save time by "speculatively" venturing down those forks. In other words, they take a guess, and execute instructions to get a head start. If the processor learns that it ventured down the wrong path, it jumps back to the fork in the road, and throws out the speculative work.

VUSEC's Bosman confirmed that when Intel processors perform that speculative execution, they don't fully segregate processes that are meant to be low-privilege and untrusted from the highest-privilege memory in the computer's kernel. That means a hacker can trick the processor into allowing unprivileged code to peek into the kernel's memory with speculative execution.