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NVD / CVE Program· CNA redhat

CVE-2021-20233: A flaw was found in grub2 in versions prior to 2.06.

Noroxi assessment

Priority: Monitor (action score 32/100)

  • Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.60% (FIRST EPSS).
  • Someone with local access to the system can trigger it. Administrator privileges are required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: shim-aa64 (AlmaLinux:8) 15.4-2.el8_1.alma; shim-ia32 (AlmaLinux:8) 15.4-2.el8_1.alma; shim-unsigned-aarch64 (AlmaLinux:8) 15-7.el8_1.alma.
  • Mentioned 2 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to shim-aa64 (AlmaLinux:8) 15.4-2.el8_1.alma; shim-ia32 (AlmaLinux:8) 15.4-2.el8_1.alma; shim-unsigned-aarch64 (AlmaLinux:8) 15-7.el8_1.alma or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

HighCVSS 8.2 · v3.1—Proof of concept Fix available
Published
Mar 3, 2021
Updated
Jun 16, 2026
EPSS
0.6% · 48th percentile

Report tools

JSON

Action score

32

Monitor

Low priority for now.

CVSS
32 / 40 · 8.2 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.6%

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • Proof of concept exists, no weaponized module
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
gnugrub2
redhatenterprise linux
redhatenterprise linux server aus
redhatenterprise linux server eus
redhatenterprise linux server tus
redhatenterprise linux workstation
fedoraprojectfedora
netappontap select deploy administration utility

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • fedoraproject fedora33
  • fedoraproject fedora34
  • gnu grub2before 2.06
  • netapp ontap select deploy administration utilityall versions
  • redhat enterprise linux7.0
  • redhat enterprise linux8.0
  • redhat enterprise linux server aus7.2
  • redhat enterprise linux server aus7.3
  • redhat enterprise linux server aus7.4
  • redhat enterprise linux server aus7.6
  • redhat enterprise linux server aus7.7
  • redhat enterprise linux server aus8.2
  • redhat enterprise linux server eus7.6
  • redhat enterprise linux server eus7.7
  • redhat enterprise linux server eus8.1
  • redhat enterprise linux server tus7.4
  • redhat enterprise linux server tus7.6
  • redhat enterprise linux server tus7.7
  • redhat enterprise linux server tus8.2
  • redhat enterprise linux workstation7.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (redhat). Independent of NVD's CPE analysis and usually ahead of it.

  • n/a grub2

    • grub 2.06affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:8shim-aa64before 15.4-2.el8_1.alma15.4-2.el8_1.alma
AlmaLinux:8shim-ia32before 15.4-2.el8_1.alma15.4-2.el8_1.alma
AlmaLinux:8shim-unsigned-aarch64before 15-7.el8_1.alma15-7.el8_1.alma
AlmaLinux:8shim-unsigned-x64before 15.4-4.el8_1.alma15.4-4.el8_1.alma
AlmaLinux:8shim-x64before 15.4-2.el8_1.alma15.4-2.el8_1.alma
Alpine:v3.17grubbefore 2.06-r02.06-r0
Debian:10grub2before 2.02+dfsg1-20+deb10u42.02+dfsg1-20+deb10u4
Debian:12grub2before 2.04-162.04-16
openSUSE:Leap 15.2grub2before 2.04-lp152.7.22.72.04-lp152.7.22.7
openSUSE:Tumbleweedgrub2before 2.06-7.12.06-7.1
Red Hat:enterprise_linux:7::clientgrub2before 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-commonbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-debuginfobefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-efi-aa64-modulesbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-efi-ia32before 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-efi-ia32-cdbootbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-efi-ia32-modulesbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-efi-x64before 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-efi-x64-cdbootbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-efi-x64-modulesbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-pcbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-pc-modulesbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-ppc-modulesbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2
Red Hat:enterprise_linux:7::clientgrub2-ppc64-modulesbefore 1:2.02-0.87.el7_9.21:2.02-0.87.el7_9.2

+96

Same product

gnu: all records

Other highest-scoring records for the same primary product.

  • CVE-2024-56737GNU GRUB (aka GRUB2) through 2.12 has a heap-based buffer overflow in fs/hfs.c via crafted sblock data in an HFS filesystem.
    35Monitor
  • CVE-2022-2601A buffer overflow was found in grub_font_construct_glyph().
    34Monitor
  • CVE-2020-10713A flaw was found in grub2, prior to version 2.06.
    33Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2020-27779Mar 3, 2021 · A flaw was found in grub2 in versions prior to 2.06.
    30Monitor
  • ← EarlierCVE-2021-20225Mar 3, 2021 · A flaw was found in grub2 in versions prior to 2.06.
    26Monitor
  • Later →CVE-2021-3418Mar 15, 2021 · If certificates that signed grub are installed into db, grub can be booted directly.
    25Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:shim-aa6415.4-2.el8_1.alma · AlmaLinux:8Package registry (OSV)
almalinux:shim-ia3215.4-2.el8_1.alma · AlmaLinux:8Package registry (OSV)
almalinux:shim-unsigned-aarch6415-7.el8_1.alma · AlmaLinux:8Package registry (OSV)
almalinux:shim-unsigned-x6415.4-4.el8_1.alma · AlmaLinux:8Package registry (OSV)
almalinux:shim-x6415.4-2.el8_1.alma · AlmaLinux:8Package registry (OSV)
alpine:grub2.06-r0 · Alpine:v3.17Package registry (OSV)
debian:grub22.04-16 · Debian:12Package registry (OSV)
opensuse:grub22.04-lp152.7.22.7 · openSUSE:Leap 15.2Package registry (OSV)
red hat:grub21:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-common1:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-debuginfo1:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-debugsource1:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-efi-aa641:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-efi-aa64-cdboot1:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-efi-aa64-modules1:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-efi-ia321:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-efi-ia32-cdboot1:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-efi-ia32-modules1:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-efi-x641:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:grub2-efi-x64-cdboot1:2.02-90.el8_3.1 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
rocky linux:fwupd0:1.5.9-1.el8_4 · Rocky Linux:8Package registry (OSV)
rocky linux:shim-unsigned-aarch640:15-7.el8.1.1 · Rocky Linux:8Package registry (OSV)
suse:grub22.02-115.59.1 · SUSE:OpenStack Cloud 7Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

  • Proof-of-concept repository on GitHub ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHubstars:02022-07-19

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. First PoC+502 d
  3. TodayOct 26, 2026+2063 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • Administrator privileges are required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted

Impact can extend beyond the vulnerable component (scope changes).

Attack vector
Local
Attack complexity
Low
Privileges required
High
User interaction
None
Scope
Changed
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-787 · Out-of-bounds Write

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records