CVE-2021-3418

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.

Published: 2021-03-15 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3418 is rated Low Risk (39.1/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.48%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-3418

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.06% 0.48% +0.42%
2 2025-11-21 0.03% 0.06% +0.04%
3 2025-11-18 — 0.03% —

Full EPSS history (11 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3418

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.4 3.1 MEDIUM
CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:H)
They need powerful rights—admin, root, or similar—before this pays off.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 0.5 5.9 [email protected]
4.4 2.0 MEDIUM
AV:L/AC:M/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 3.4 6.4 [email protected]

Weakness enumeration for CVE-2021-3418

OS Trackers for CVE-2021-3418

vendor priority summary link
alpine medium CVE-2021-3418: 1 source package rows (grub); 7 state rows across 7 repos (3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 7, open 0. https://security.alpinelinux.org/vuln/CVE-2021-3418
debian unimportant CVE-2021-3418 unimportant priority: Debian including 1 source packages (grub2), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3418
redhat medium — https://access.redhat.com/security/cve/CVE-2021-3418
suse medium CVE-2021-3418 severity moderate: SUSE including 9 source package names (grub2, grub2-arm64-efi, …), 199 product×package rows across 39 product lines (HPE Helion OpenStack 8, SUSE CaaS Platform 4.0, … (39 product lines)): Known Not Affected 199. https://www.suse.com/security/cve/CVE-2021-3418/
ubuntu medium CVE-2021-3418 medium priority: Ubuntu including 3 source packages (grub2, grub2-signed, grub2-unsigned), 27 status rows across 9 suites (bionic, focal, groovy, hirsute, impish, jammy, trusty, upstream, xenial): not-affected 24, needs-triage 2, DNE 1. https://ubuntu.com/security/CVE-2021-3418

Affected software / configurations for CVE-2021-3418

Vendor Product Version Raw CPE
gnu grub2 < 2.06 cpe:2.3:a:gnu:grub2:*:*:*:*:*:*:*:*

References for CVE-2021-3418

URL Tags
https://bugzilla.redhat.com/show_bug.cgi?id=1933757 Issue Tracking Third Party Advisory
cvelogic Threat Intelligence