CVE-2021-20233

Code execution via quoted-character length miscalculation

Published Mar 3, 2021 · Updated Aug 3, 2024

Heap out-of-bounds write in GNU GRUB before 2.06 allows local users to execute arbitrary code through crafted menu input. Setparam_prefix() reserves three characters for each quoted single quote although rendering requires four, producing a one-byte heap overwrite per quote. Exploitation requires local high privileges and crafted input processed during menu rendering, enabling code execution and UEFI Secure Boot bypass.

CVSS severity7.5
High
EPSS probability0.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap out-of-bounds write in GNU GRUB before 2.06 allows local users to execute arbitrary code through crafted menu input. Setparam_prefix() reserves three characters for each quoted single quote although rendering requires four, producing a one-byte heap overwrite per quote. Exploitation requires local high privileges and crafted input processed during menu rendering, enabling code execution and UEFI Secure Boot bypass.

The record

CVE
CVE-2021-20233
Published
Mar 3, 2021
Updated
Aug 3, 2024
Vendor
The GnuPG Project
Product
GNU GRUB
Classifications
CWE-787, T1068
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Mar 3, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=grub 2.06

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The GnuPG Project · GNU GRUBversion=grub 2.06

Published CVSS scores

7.5GNU GRUB ProjectCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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