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Fencer Vulns
medium 6.4

CVE-2021-20261 json

A race condition was found in the Linux kernels implementation of the floppy disk drive controller driver software.

published 2021-03-11 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-7698

cvss
6.4
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits
0
none known

Summary

A race condition was found in the Linux kernels implementation of the floppy disk drive controller driver software. The impact of this issue is lessened by the fact that the default permissions on the floppy device (/dev/fd0) are restricted to root. If the permissions on the device have changed the impact changes greatly. In the default configuration root (or equivalent) permissions are required to attack this flaw.

Patch / fix

  • linux linux_kernel 4.5
  • linux Debian 14, Debian 13, Debian 12 4.5.1-1

debian advisories DEBIAN-CVE-2021-20261

  • linux Ubuntu 16.04 LTS 4.4.0-208.240
  • linux-aws Ubuntu 16.04 LTS 4.4.0-1126.140
  • linux-kvm Ubuntu 16.04 LTS 4.4.0-1091.100
  • linux-raspi2 Ubuntu 16.04 LTS 4.4.0-1150.161
  • linux-snapdragon Ubuntu 16.04 LTS 4.4.0-1154.164
  • linux-snapdragon Ubuntu 18.04 LTS 4.15.0-1053.57
  • linux-aws Ubuntu Pro 14.04 LTS 4.4.0-1090.94
  • linux-fips Ubuntu Pro FIPS-updates 16.04 LTS 4.4.0-1060.66

ubuntu advisories UBUNTU-CVE-2021-20261

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-ec2 SLES 11 SP4-LTSS 3.0.101-108.126.1
  • kernel-pae SLES 11 SP4-LTSS 3.0.101-108.126.1
  • kernel-xen SLES 11 SP4-LTSS 3.0.101-108.126.1
  • kernel-syms SLES 11 SP4-LTSS 3.0.101-108.126.1
  • kernel-ppc64 SLES 11 SP4-LTSS 3.0.101-108.126.1
  • kernel-trace SLES 11 SP4-LTSS 3.0.101-108.126.1
  • kernel-bigmem SLES 11 SP4-LTSS 3.0.101-108.126.1
  • kernel-source SLES 11 SP4-LTSS 3.0.101-108.126.1

suse advisories SUSE-SU-2021:14724-1

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-2021-20261 updated cvss 6.7

kernel: panic on multiple access to floppy device

  • Red Hat Enterprise Linux 5 kernel
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 kernel, bpftool, kernel-rt, kernel-rt-kvm, kernel-rt-trace, kernel-rt-debug-kvm, +1 more
    affected: workaround, no fix available
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, kernel-alt, python-perf, kernel-kdump, kernel-tools, +3 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more
    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

0.23% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.4 CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 4.4 AV:L/AC:M/Au:N/C:P/I:P/A:P

Affected products

  • n/a kernel

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
Technology feeds

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.