Meltdown and Spectre are two vulnerabilities discovered by Google security researchers that affect almost all CPUs released since 1995, impacting CPUs deployed in desktops, laptops, servers, smartphones, smart devices, and cloud services.
Researchers say that attackers can use the two flaws to read data from a computer's kernel memory (Meltdown), but also data handled by other apps (Spectre).
More precisely, Google says the two bugs can be exploited to "to steal data which is currently processed on the computer," which includes "your passwords stored in a password manager or browser, your personal photos, emails, instant messages and even business-critical documents."
In research published online late last night, Google didn't provide specific ways in which an attack could take place, but many security experts that looked over the Meltdown and Spectre academic papers said that web-based attacks are possible, and not just attacks using locally-delivered malicious code.
"Our internal experiments confirm that it is possible to use similar techniques from Web content to read private information between different origins," said Luke Wagner, a software engineer with the Mozilla Foundation.
Details about the Meltdown and Spectre flaws had been shared with Mozilla since last year, and Wagner says Firefox 57.x branches will receive countermeasures.
Both Meltdown and Spectre are side-channel attacks that produce leak memory data. They both rely on the ability to very precisely measure time to deliver exploits that leak memory data.
To hinder the attacks' efficiency, Mozilla says it will reduce the precision of Firefox's internal timer functions. This is not a full mitigation, but just an efficient and clever workaround.
Mozilla said it will experiment with new mitigation techniques that will "remove the information leak closer to the source, instead of just hiding the leak by disabling timers."
According to Google, Chrome will also receive mitigations to protect against Meltdown and Spectre exploitation in Chrome 64, due to be released on January 23.
Until then, Google recommends that users enable a new security feature it shipped in Chrome 63, called Strict Site Isolation.
Microsoft has also released updates for Edge and Internet Explorer, that are part of an out-of-band update for Windows operating systems, released yesterday.
Despite this, some experts argue that Meltdown and Spectre are two vulnerabilities that are most likely to be exploited in targeted attacks against specific targets, rather than in en-masse, non-discriminatory campaigns.
Any idea on whether Meltdown/Spectre will ever be exploited at scale? Reading memory *and* doing something useful with it doesn't tend to scale well for attackers. Remember that Heartbleed was never exploited at scale.— Martijn Grooten (@martijn_grooten) January 4, 2018
UPDATE: Mozilla has released Firefox 57.0.4 that includes Meltdown and Spectre mitigations.