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Fencer Intel
medium 4.7

CVE-2021-20321 json

A race condition accessing file object in the Linux kernel OverlayFS subsystem was found in the way users do rename in specific way with Ov…

published 4y ago modified 4mo ago also EUVD-2021-7745

cvss
4.7
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 12%
public exploits
0
none known

Summary

A race condition accessing file object in the Linux kernel OverlayFS subsystem was found in the way users do rename in specific way with OverlayFS. A local user could use this flaw to crash the system.

Patch / fix

  • linux linux_kernel 5.15
  • linux Debian 14, Debian 13, Debian 12 5.14.12-1

debian advisories DEBIAN-CVE-2021-20321

  • linux Ubuntu 18.04 LTS 4.15.0-166.174
  • linux Ubuntu 20.04 LTS 5.4.0-92.103
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1118.125
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1061.64
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1059.63
  • linux-gke Ubuntu 20.04 LTS 5.4.0-1057.60
  • linux-ibm Ubuntu 20.04 LTS 5.4.0-1010.11
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1105.107

ubuntu advisories UBUNTU-CVE-2021-20321

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 RHEL 8 4.18.0-348.7.1.el8_5
  • perf RHEL 8 4.18.0-348.7.1.el8_5
  • bpftool RHEL 8 4.18.0-348.7.1.el8_5
  • kernel-core RHEL 8 4.18.0-348.7.1.el8_5
  • kernel-tools RHEL 8 4.18.0-348.7.1.el8_5
  • python3-perf RHEL 8 4.18.0-348.7.1.el8_5
  • kernel-modules RHEL 8 4.18.0-348.7.1.el8_5
  • kernel-zfcpdump RHEL 8 4.18.0-348.7.1.el8_5

red hat advisories RHSA-2021:5227RHSA-2021:5241

  • kernel-syms SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +3 more 4.12.14-150100.197.114.2
  • kernel-source SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +3 more 4.12.14-150100.197.114.2
  • kernel-default SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +7 more 4.12.14-150100.197.114.2
  • kernel-vanilla openSUSE Leap 15.4, openSUSE Leap 15.3 4.12.14-150100.197.114.2
  • kernel-kvmsmall openSUSE Leap 15.4, openSUSE Leap 15.3 4.12.14-150100.197.114.2
  • kernel-zfcpdump SLES 15 SP1-LTSS, openSUSE Leap 15.4, openSUSE Leap 15.3 4.12.14-150100.197.114.2
  • kernel-obs-build SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +3 more 4.12.14-150100.197.114.2
  • kernel-syms SLES for SAP 15 SP2, SLES 15 SP2-LTSS, SLES 15 SP2-BCL +6 more 5.3.18-150200.24.115.1

suse advisories SUSE-SU-2022:2111-1SUSE-SU-2022:2104-1SUSE-SU-2022:2103-1SUSE-SU-2022:2083-1SUSE-SU-2022:2082-1SUSE-SU-2022:2077-1

  • kernel-rt Rocky Linux 8 4.18.0-348.7.1.rt7.137.el8_5
  • kernel Rocky Linux 8 4.18.0-348.7.1.el8_5

rocky linux advisories RLSA-2021:5241RLSA-2021:5227

  • linux Arch Linux 5.14.12.arch1-1
  • linux-zen Arch Linux 5.14.12.zen1-1
  • linux-hardened Arch Linux 5.14.13.hardened1-1
  • linux-lts Arch Linux 5.10.73-1

arch linux advisories AVG-2463AVG-2464AVG-2465AVG-2466

Is CVE-2021-20321 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

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-2021-20321 updated cvss 5.5

kernel: In Overlayfs missing a check for a negative dentry before calling vfs_rename()

  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat CodeReady Linux Builder (v. 8) kernel-debuginfo-common-x86_64 4.18.0-348.7.1.el8_5, kernel-debuginfo-common-aarch64 4.18.0-348.7.1.el8_5, kernel-debuginfo-common-ppc64le 4.18.0-348.7.1.el8_5 Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-348.7.1.el8_5, kernel 4.18.0-348.7.1.el8_5, bpftool 4.18.0-348.7.1.el8_5, kernel-core 4.18.0-348.7.1.el8_5, kernel-tools 4.18.0-348.7.1.el8_5, python3-perf 4.18.0-348.7.1.el8_5, +15 more
    fixed: vendor fix RHSA-2021:5227
  • Red Hat Enterprise Linux for Real Time (v. 8) kernel-rt 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-core 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-modules 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-debug-core 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-debug-modules 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-modules-extra 4.18.0-348.7.1.rt7.137.el8_5, +2 more Red Hat Enterprise Linux Real Time for NFV (v. 8) kernel-rt 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-kvm 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-core 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-modules 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-debug-kvm 4.18.0-348.7.1.rt7.137.el8_5, kernel-rt-debug-core 4.18.0-348.7.1.rt7.137.el8_5, +4 more
    fixed: vendor fix RHSA-2021:5241
  • Red Hat Enterprise Linux 5 kernel Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more Red Hat Enterprise Linux BaseOS (v. 8) kernel-headers 4.18.0-348.7.1.el8_5
    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

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.7 AV:L/AC:M/Au:N/C:N/I:N/A:C

Affected products

  • n/a kernel

Classification

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

References

Sources

Fencer Intel 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.