Meltdown (CVE-2017-5754) breaks the isolation between user applications and the operating system. Spectre (CVE-2017-5753 and CVE-2017-5715) breaks isolation between applications by tricking well-written programs into leaking their own secrets. Meltdown has operating system patches. Spectre is harder to fix and needs several kinds of mitigation.
What they have in common
Both are hardware level issues in modern processors, described on the researchers' site meltdownattack.com. Both let a program read data it should not be able to access. The root cause lies in how processors speculate ahead to run faster, and the side effects of that work can be observed.
You cannot patch a CPU's design in the way you patch a library, so fixes come in layers: operating system changes, compiler changes and, in some cases, microcode or firmware from the vendor.
Meltdown
According to the site, Meltdown breaks the most fundamental isolation between user applications and the operating system. A program can read memory belonging to other programs and to the OS. It was verified on Intel processors, with some ARM processors also affected.
Fix: software patches exist for Linux, where the technique is called KPTI (formerly KAISER), and for Windows and OS X. These change how the kernel's memory is mapped so user code cannot see it.
Spectre
Spectre breaks isolation between applications. It is described as tricking correctly written programs into leaking secrets. The site says it affects nearly all systems, including desktops, laptops, servers and smartphones, and it was verified on Intel, AMD and ARM processors.
Fix: harder. Patches can block specific known exploits, and compilers were updated to harden software, with changes listed in LLVM, MSVC and an ARM speculation barrier header. There is no single switch that ends the issue.
What could be exposed
The researchers list passwords in password managers or browsers, personal photos, emails, instant messages and business documents. In cloud environments, data of other customers could be exposed depending on the provider, and the site notes risk where kernels are shared, such as with some container technologies.
Practical guidance for engineering teams
- Keep operating systems and hypervisors current. Meltdown mitigations arrive through OS updates.
- Apply firmware and microcode updates from your hardware vendor when they are offered.
- Rebuild with updated compilers where the vendor recommends it for sensitive code.
- Treat shared hosts with care. Do not run untrusted code beside sensitive workloads on the same kernel or host if you can avoid it.
- Measure performance after patching. Some mitigations change performance, so test before a broad rollout.
What to keep in mind
Not every vulnerability can be closed with one upgrade. Hardware issues stay in the environment for years, so the useful questions are about isolation: what runs beside what, and what could it read? Safeguard's asset discovery can help you see which systems you operate, though hardware level patching remains with your OS and vendor channels.
Quick check
Which one has straightforward OS patches?
Meltdown, through changes such as KPTI on Linux. Spectre is harder to fix.
Do they affect only Intel chips?
No. Meltdown was verified on Intel with some ARM affected. Spectre was verified on Intel, AMD and ARM.
Sources
Last reviewed: 19 October 2026.
