What is CVE-2021-20233?

CVE-2021-20233 is a high-severity vulnerability in GNU Grub2, classified under Out-of-bounds Write. CVSS score: 8.2/10. Published 2021-03-03.

How severe is CVE-2021-20233?

High severity. CVSS v3 base score is 8.2 out of 10.

Is CVE-2021-20233 known to be exploited?

36 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Buffer overflow in GNU Grub2

CVE-2021-20233

A flaw was found in grub2 in versions prior to 2.06. Setparam_prefix() in the menu rendering code performs a length calculation on the assumption that expressing a quoted single quote will require 3 characters, while it actually requires 4 characters which allows an attacker to corrupt memory by one byte for each quote in the input. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

Vulnerability class: Buffer Overflow

Published 2021-03-03 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.2 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.006 (48.0th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 48th percentile — 48.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

GNU Grub2
NetApp Ontap Select Deploy Administration Utility
Fedoraproject Fedora — versions 33, 34
Red Hat Enterprise Linux — versions 7.0, 8.0
Red Hat Enterprise Linux Server Aus — versions 7.2, 7.3, 7.4
Red Hat Enterprise Linux Server Eus — versions 7.6, 7.7, 8.1
Red Hat Enterprise Linux Server Tus — versions 7.4, 7.6, 7.7
Red Hat Enterprise Linux Workstation — versions 7.0
Grub2 — versions grub 2.06

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

Public proof-of-concept exploits

References

bugzilla.redhat.com/show_bug.cgi (Patch, Third Party Advisory, Issue Tracking)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
security.gentoo.org/glsa/202104-05 (vendor-advisory, Third Party Advisory)
security.netapp.com/advisory/ntap-20220325-0001/ (Third Party Advisory)

Frequently asked questions

What is CVE-2021-20233?: CVE-2021-20233 is a high-severity vulnerability in GNU Grub2, classified under Out-of-bounds Write. CVSS score: 8.2/10. Published 2021-03-03.
How severe is CVE-2021-20233?: High severity. CVSS v3 base score is 8.2 out of 10.
Is CVE-2021-20233 known to be exploited?: 36 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.