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Fencer Vulns
medium 4.6

CVE-2021-34557 json

XScreenSaver 5.45 can be bypassed if the machine has more than ten disconnectable video outputs.

published 2021-06-10 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-21207

cvss
4.6
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 41%
public exploits
0
none known

Summary

XScreenSaver 5.45 can be bypassed if the machine has more than ten disconnectable video outputs. A buffer overflow in update_screen_layout() allows an attacker to bypass the standard screen lock authentication mechanism by crashing XScreenSaver. The attacker must physically disconnect many video outputs.

Patch / fix

  • xscreensaver Debian 14, Debian 13, Debian 12 5.45+dfsg1-2

debian advisories DEBIAN-CVE-2021-34557

  • xscreensaver SLES for SAP 12 SP5, SLES 12 SP5 5.22-8.3.1
  • xscreensaver SLE Module for Basesystem 15 SP3, openSUSE Leap 15.3 5.44-150000.5.6.1

suse advisories SUSE-SU-2022:2642-1SUSE-SU-2022:2641-1

  • xscreensaver Alpine 3.24, Alpine 3.23, Alpine 3.22 +6 more 6.02-r0

alpine advisories ALPINE-CVE-2021-34557

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-34557 updated cvss 6.4

XScreenSaver: buffer overflow in update_screen_layout() allows an attacker to bypass the standard screen lock authentication

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.48% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • openwall.com https://www.openwall.com/lists/oss-security/2021/06/05/1 referenced PoC, tagged "exploit" by a source, unverified
  • github.com https://github.com/QubesOS/qubes-secpack/blob/master/QSBs/qsb-068-2021.txt referenced PoC, tagged "exploit" by a source, unverified
  • openwall.com http://www.openwall.com/lists/oss-security/2021/07/06/2 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 4.6 CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:N/I:N/A:P

Classification

Weakness
  • CWE-120 Buffer Copy without Checking Size of Input

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.