CVE-2021-3567Public exploit

Screen-lock bypass via malformed XKB map update

Published Mar 25, 2022 · Updated Aug 3, 2024

An input-validation flaw in GNOME Caribou 0.4.21 allows physically proximate attackers to bypass a Cinnamon screen lock via shifted input. The X11 adapter includes XkbKeyTypesMask and key-type fields in XkbChangeMap while changing only key symbols, provoking a BadLength error and crash after the Xorg fix. The bypass requires Cinnamon Screensaver 4.2 or later with Caribou enabled; crashing the keyboard also terminates the lock screen and exposes the active session without a password.

CVSS severity7.5
High
EPSS probability1.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

An input-validation flaw in GNOME Caribou 0.4.21 allows physically proximate attackers to bypass a Cinnamon screen lock via shifted input. The X11 adapter includes XkbKeyTypesMask and key-type fields in XkbChangeMap while changing only key symbols, provoking a BadLength error and crash after the Xorg fix. The bypass requires Cinnamon Screensaver 4.2 or later with Caribou enabled; crashing the keyboard also terminates the lock screen and exposes the active session without a password.

The record

CVE
CVE-2021-3567
Published
Mar 25, 2022
Updated
Aug 3, 2024
Vendor
GNOME
Product
Caribou
Classifications
CWE-20, CWE-787, T1068
Attack vector
physical
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 25, 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=caribou 0.4.21

What conditions does exploitation require?

Attack vectorphysical
Required privilegesunauthenticated

What is affected?

GNOME · Caribouversion=caribou 0.4.21

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

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.

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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)
Vectorphysical
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
CWE-787Out-of-bounds Write
T1068Exploitation for Privilege Escalation

Public exploit references

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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