Is CVE-2021-20233 in the CISA KEV catalog?

No. CVE-2021-20233 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-20233?

CVE-2021-20233 has a CVSS v3 base score of 8.2 (HIGH).

What is the EPSS score for CVE-2021-20233?

CVE-2021-20233 has an EPSS score of 0.61% (45th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-20233?

Upgrade grub2 on debian 11 to 2.04-16 or later. Fixes are available for 7 affected products.

CVE & CISA-KEV Catalog

CVE-2021-20233

HIGH

8.2

CVSS v3

NVD

Description

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.

CWE-787Out-of-bounds Write

How to fix

Remediation Available

grub2Debian

Fixed in:2.04-16CVE-2021-20233

grub-efi-amd64-binUbuntu

Fixed in:2.04-1ubuntu44.1.2USN-4992-1

Fixed in:2.04-1ubuntu44.2USN-4992-1

grub-efi-amd64-signedUbuntu

Fixed in:1.167~18.04.5+2.04-1ubuntu44.1.2USN-4992-1

Fixed in:1.167.2+2.04-1ubuntu44.2USN-4992-1

grub-efi-arm64-binUbuntu

Fixed in:2.04-1ubuntu44.1.2USN-4992-1

Fixed in:2.04-1ubuntu44.2USN-4992-1

grub-efi-arm64-signedUbuntu

Fixed in:1.167~18.04.5+2.04-1ubuntu44.1.2USN-4992-1

Fixed in:1.167.2+2.04-1ubuntu44.2USN-4992-1

grub2-signedUbuntu

Fixed in:1.167~18.04.5USN-4992-1

Fixed in:1.167.2USN-4992-1

grub2-unsignedUbuntu

Fixed in:2.04-1ubuntu44.1.2USN-4992-1

Fixed in:2.04-1ubuntu44.2USN-4992-1

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorLocal

Attack ComplexityLow

Privileges RequiredHigh

User InteractionNone

ScopeChanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

Exploit Intelligence

0.61%probability of exploitation in 30 days

45thpercentile

Moderate risk: more likely to be exploited than 45% of all known CVEs.

References

Patch1

bugzilla.redhat.com

Third-Party Advisory2

Other references1

lists.fedoraproject.org

Related Vulnerabilities

Other CWE-787 (Out-of-bounds Write) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-22457	Critical	9.0	100%	KEV + Ransom	Fix
CVE-2025-0282	Critical	9.0	100%	KEV + Ransom	-
CVE-2015-3113	Critical	9.8	100%	KEV	Fix
CVE-2021-20038	Critical	9.8	100%	KEV + Ransom	-
CVE-2023-4863	High	8.8	100%	KEV	Fix
CVE-2020-16040	Medium	6.5	100%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.