CVE-2021-33656

System crash via VGA font out-of-bounds write

Published Jul 18, 2022 · Updated Aug 3, 2024

Out-of-bounds write in the Linux kernel virtual terminal driver before 5.10.127 allows physically proximate attackers to crash the system. The legacy PIO_FONT ioctl sends attacker-controlled VGA font data into console font handling, where malformed values cause a kernel memory write beyond the intended buffer. Triggering requires access to a text-mode console backed by a generic VGA display; Ubuntu also identifies arbitrary code execution as possible.

CVSS severity6.8
Medium
EPSS probability0.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in the Linux kernel virtual terminal driver before 5.10.127 allows physically proximate attackers to crash the system. The legacy PIO_FONT ioctl sends attacker-controlled VGA font data into console font handling, where malformed values cause a kernel memory write beyond the intended buffer. Triggering requires access to a text-mode console backed by a generic VGA display; Ubuntu also identifies arbitrary code execution as possible.

The record

CVE
CVE-2021-33656
Published
Jul 18, 2022
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-787, T1068
Attack vector
physical
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 18, 2022CVE 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<5.10.127

What conditions does exploitation require?

Attack vectorphysical
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=<5.10.127

Published CVSS scores

6.8NIST National Vulnerability DatabaseCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorphysical
Privilegesunauthenticated
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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