CVE-2021-34557Public exploit

Physical screen-lock bypass via output-array over-read

Published Jun 10, 2021 · Updated Aug 4, 2024

Out-of-bounds read in XScreenSaver 5.45 allows physically proximate attackers to bypass screen-lock authentication by disconnecting displays. The update_screen_layout() function sizes its screen-information array from connected outputs but later iterates over every defined output, reading beyond the allocation and passing unrelated memory to XDeleteProperty as a window ID. More than ten disconnectable outputs and physical access to a locked X11 session are required; the resulting invalid-window error crashes XScreenSaver and leaves the desktop unlocked.

CVSS severity4.6
Medium
EPSS probability0.48%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Out-of-bounds read in XScreenSaver 5.45 allows physically proximate attackers to bypass screen-lock authentication by disconnecting displays. The update_screen_layout() function sizes its screen-information array from connected outputs but later iterates over every defined output, reading beyond the allocation and passing unrelated memory to XDeleteProperty as a window ID. More than ten disconnectable outputs and physical access to a locked X11 session are required; the resulting invalid-window error crashes XScreenSaver and leaves the desktop unlocked.

The record

CVE
CVE-2021-34557
Published
Jun 10, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-120
Attack vector
physical
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorphysical
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.6NIST NVDCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
2.1NIST NVDAV:L/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.

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

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-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

Public exploit references

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo