The Meltdown and Spectre flaws—two related vulnerabilities that enable a wide range of information disclosure from every mainstream processor, with particularly severe flaws for Intel and some ARM chips—were originally revealed privately to chip companies, operating system developers, and cloud computing providers. That private disclosure was scheduled to become public some time next week, enabling these companies to develop (and, in the case of the cloud companies, deploy) suitable patches, workarounds, and mitigations.

With researchers figuring out one of the flaws ahead of that planned reveal, that schedule was abruptly brought forward, and the pair of vulnerabilities was publicly disclosed on Wednesday, prompting a rather disorderly set of responses from the companies involved.

There are three main groups of companies responding to the Meltdown and Spectre pair: processor companies, operating system companies, and cloud providers. Their reactions have been quite varied.

What Meltdown and Spectre do

A brief recap of the problem: modern processors perform speculative execution. To maximize performance, they try to execute instructions even before it is certain that those instructions need to be executed. For example, the processors will guess at which way a branch will be taken and execute instructions on the basis of that guess. If the guess is correct, great; the processor got some work done without having to wait to see if the branch was taken or not. If the guess is wrong, no big deal; the results are discarded and the processor resumes executing the correct side of the branch.

While this speculative execution does not alter program behavior at all, the Spectre and Meltdown research demonstrates that it perturbs the processor’s state in detectable ways. This perturbation can be detected by carefully measuring how long it takes to perform certain operations. Using these timings, it’s possible for one process to infer properties of data belonging to another process—or even the operating system kernel or virtual machine hypervisor.

This information leakage can be used directly; for example, a malicious JavaScript in a browser could steal passwords stored in the browser. It can also be used in tandem with other security flaws to increase their impact. Information leakage tends to undermine protections such as ASLR (address space layout randomization), so these flaws may enable effective exploitation of buffer overflows.

Meltdown, applicable to virtually every Intel chip made for many years, along with certain high-performance ARM designs, is the easier to exploit and enables any user program to read vast tracts of kernel data. The good news, such as it is, is that Meltdown also appears easier to robustly guard against. The flaw depends on the way that operating systems share memory between user programs and the kernel, and the solution—albeit a solution that carries some performance penalty—is to put an end to that sharing.

Spectre, applicable to chips from Intel, AMD, and ARM, and probably every other processor on the market that offers speculative execution, too, is more subtle. It encompasses a trick testing array bounds to read memory within a single process, which can be used to attack the integrity of virtual machines and sandboxes, and cross-process attacks using the processor’s branch predictors (the hardware that guesses which side of a branch is taken and hence controls the speculative execution). Systemic fixes for some aspects of Spectre appear to have been developed, but protecting against the whole range of fixes will require modification (or at least recompilation) of at-risk programs.