7.7 KiB

Spectre & Meltdown Checker

A shell script to tell if your system is vulnerable against the several "speculative execution" CVEs that were made public since 2018.

  • CVE-2017-5753 [bounds check bypass] aka 'Spectre Variant 1'
  • CVE-2017-5715 [branch target injection] aka 'Spectre Variant 2'
  • CVE-2017-5754 [rogue data cache load] aka 'Meltdown' aka 'Variant 3'
  • CVE-2018-3640 [rogue system register read] aka 'Variant 3a'
  • CVE-2018-3639 [speculative store bypass] aka 'Variant 4'
  • CVE-2018-3615 [L1 terminal fault] aka 'Foreshadow (SGX)'
  • CVE-2018-3620 [L1 terminal fault] aka 'Foreshadow-NG (OS)'
  • CVE-2018-3646 [L1 terminal fault] aka 'Foreshadow-NG (VMM)'
  • CVE-2018-12126 [microarchitectural store buffer data sampling (MSBDS)] aka 'Fallout'
  • CVE-2018-12130 [microarchitectural fill buffer data sampling (MFBDS)] aka 'ZombieLoad'
  • CVE-2018-12127 [microarchitectural load port data sampling (MLPDS)] aka 'RIDL'
  • CVE-2019-11091 [microarchitectural data sampling uncacheable memory (MDSUM)] aka 'RIDL'

Supported operating systems:

  • Linux (all versions, flavors and distros)
  • BSD (FreeBSD, NetBSD, DragonFlyBSD)

Supported architectures:

  • x86 (32 bits)
  • amd64/x86_64 (64 bits)
  • ARM and ARM64
  • other architectures will work, but mitigations (if they exist) might not always be detected

For Linux systems, the script will detect mitigations, including backported non-vanilla patches, regardless of the advertised kernel version number and the distribution (such as Debian, Ubuntu, CentOS, RHEL, Fedora, openSUSE, Arch, ...), it also works if you've compiled your own kernel.

For BSD systems, the detection will work as long as the BSD you're using supports cpuctl and linprocfs (this is not the case of OpenBSD for example).

Easy way to run the script

  • Get the latest version of the script using curl or wget
curl -L https://meltdown.ovh -o spectre-meltdown-checker.sh
wget https://meltdown.ovh -O spectre-meltdown-checker.sh
  • Inspect the script. You never blindly run scripts you downloaded from the Internet, do you?
vim spectre-meltdown-checker.sh
  • When you're ready, run the script as root
chmod +x spectre-meltdown-checker.sh
sudo ./spectre-meltdown-checker.sh

Run the script in a docker container

With docker-compose

docker-compose build
docker-compose run --rm spectre-meltdown-checker

Without docker-compose

docker build -t spectre-meltdown-checker .
docker run --rm --privileged -v /boot:/boot:ro -v /dev/cpu:/dev/cpu:ro -v /lib/modules:/lib/modules:ro spectre-meltdown-checker

Example of script output

  • Intel Haswell CPU running under Ubuntu 16.04 LTS


  • AMD Ryzen running under OpenSUSE Tumbleweed


  • Batch mode (JSON flavor)


Quick summary of the CVEs

CVE-2017-5753 bounds check bypass (Spectre Variant 1)

  • Impact: Kernel & all software
  • Mitigation: recompile software and kernel with a modified compiler that introduces the LFENCE opcode at the proper positions in the resulting code
  • Performance impact of the mitigation: negligible

CVE-2017-5715 branch target injection (Spectre Variant 2)

  • Impact: Kernel
  • Mitigation 1: new opcode via microcode update that should be used by up to date compilers to protect the BTB (by flushing indirect branch predictors)
  • Mitigation 2: introducing "retpoline" into compilers, and recompile software/OS with it
  • Performance impact of the mitigation: high for mitigation 1, medium for mitigation 2, depending on your CPU

CVE-2017-5754 rogue data cache load (Meltdown)

  • Impact: Kernel
  • Mitigation: updated kernel (with PTI/KPTI patches), updating the kernel is enough
  • Performance impact of the mitigation: low to medium

CVE-2018-3640 rogue system register read (Variant 3a)

  • Impact: TBC
  • Mitigation: microcode update only
  • Performance impact of the mitigation: negligible

CVE-2018-3639 speculative store bypass (Variant 4)

  • Impact: software using JIT (no known exploitation against kernel)
  • Mitigation: microcode update + kernel update making possible for affected software to protect itself
  • Performance impact of the mitigation: low to medium

CVE-2018-3615 l1 terminal fault (Foreshadow-NG SGX)

  • Impact: Kernel & all software (any physical memory address in the system)
  • Mitigation: microcode update
  • Performance impact of the mitigation: negligible

CVE-2018-3620 l1 terminal fault (Foreshadow-NG SMM)

  • Impact: Kernel & System management mode
  • Mitigation: updated kernel (with PTE inversion)
  • Performance impact of the mitigation: negligible

CVE-2018-3646 l1 terminal fault (Foreshadow-NG VMM)

  • Impact: Virtualization software and Virtual Machine Monitors
  • Mitigation: disable ept (extended page tables), disable hyper-threading (SMT), or updated kernel (with L1d flush)
  • Performance impact of the mitigation: low to significant

CVE-2018-12126 [MSBDS] Microarchitectural Store Buffer Data Sampling (Fallout)

CVE-2018-12130 [MFBDS] Microarchitectural Fill Buffer Data Sampling (ZombieLoad)

CVE-2018-12127 [MLPDS] Microarchitectural Load Port Data Sampling (RIDL)

CVE-2019-11091 [MDSUM] Microarchitectural Data Sampling Uncacheable Memory (RIDL)

  • Note: These 4 CVEs are similar and collectively named "MDS" vulnerabilities, the mitigation is identical for all
  • Impact: Kernel
  • Mitigation: microcode update + kernel update making possible to protect various CPU internal buffers from unprivileged speculative access to data
  • Performance impact of the mitigation: low to significant

Understanding what this script does and doesn't

This tool does its best to determine whether your system is immune (or has proper mitigations in place) for the collectively named "speculative execution" vulnerabilities. It doesn't attempt to run any kind of exploit, and can't guarantee that your system is secure, but rather helps you verifying whether your system has the known correct mitigations in place. However, some mitigations could also exist in your kernel that this script doesn't know (yet) how to detect, or it might falsely detect mitigations that in the end don't work as expected (for example, on backported or modified kernels).

Your system exposure also depends on your CPU. As of now, AMD and ARM processors are marked as immune to some or all of these vulnerabilities (except some specific ARM models). All Intel processors manufactured since circa 1995 are thought to be vulnerable, except some specific/old models, such as some early Atoms. Whatever processor one uses, one might seek more information from the manufacturer of that processor and/or of the device in which it runs.

The nature of the discovered vulnerabilities being quite new, the landscape of vulnerable processors can be expected to change over time, which is why this script makes the assumption that all CPUs are vulnerable, except if the manufacturer explicitly stated otherwise in a verifiable public announcement.

Please also note that for Spectre vulnerabilities, all software can possibly be exploited, this tool only verifies that the kernel (which is the core of the system) you're using has the proper protections in place. Verifying all the other software is out of the scope of this tool. As a general measure, ensure you always have the most up to date stable versions of all the software you use, especially for those who are exposed to the world, such as network daemons and browsers.

This tool has been released in the hope that it'll be useful, but don't use it to jump to conclusions about your security.