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Fencer Intel
medium 6.4

CVE-2021-3418 json

If certificates that signed grub are installed into db, grub can be booted directly.

published 5y ago modified 4mo ago also EUVD-2021-26746

cvss
6.4
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits
0
none known

Summary

If certificates that signed grub are installed into db, grub can be booted directly. It will then boot any kernel without signature validation. The booted kernel will think it was booted in secureboot mode and will implement lockdown, yet it could have been tampered. This flaw is a reintroduction of CVE-2020-15705 and only affects grub2 versions prior to 2.06 and upstream and distributions using the shim_lock mechanism.

Patch / fix

  • gnu grub2 2.06
  • grub Alpine 3.24, Alpine 3.23, Alpine 3.22 +5 more 2.06-r0

alpine advisories ALPINE-CVE-2021-3418

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • grub2 CBL-Mariner 2.0 2.06~rc1-7

azure linux advisories AZL-6467

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3418 updated cvss 6.4

grub2: grub 2.05 reintroduced CVE-2020-15705

  • Red Hat Enterprise Linux 7 grub2, grub2-pc, grub2-efi, grub2-ppc64, grub2-tools, grub2-common, +15 more Red Hat Enterprise Linux 8 grub2, grub2-pc, grub2-tools, grub2-common, grub2-efi-x64, grub2-ppc64le, +13 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.47% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 6.4 CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 4.4 AV:L/AC:M/Au:N/C:P/I:P/A:P

Affected products

  • n/a grub2

Classification

Weakness
  • CWE-281 Improper Preservation of Permissions

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.