CVE-2021-20321

Severity: medium (CVSS 4.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2022-02-18 · updated 2026-06-17
Weakness: CWE-362

Description

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.

Affected products

Debian Linux: 9.0, 10.0
Linux kernel: before 5.15; 5.15, 5.15-rc1, 5.15-rc2, 5.15-rc3, 5.15-rc4 — fixed in 5.15
Red Hat Enterprise Linux: 7.0, 8.0

How to fix

Upgrade to a fixed version: Linux kernel 5.15. Check the vendor advisory for mitigations.

References

https://bugzilla.redhat.com/show_bug.cgi?id=2013242
https://lists.debian.org/debian-lts-announce/2022/03/msg00012.html
https://lore.kernel.org/all/20211011134508.748956131%40linuxfoundation.org/
https://www.debian.org/security/2022/dsa-5096
https://bugzilla.redhat.com/show_bug.cgi?id=2013242
https://lists.debian.org/debian-lts-announce/2022/03/msg00012.html
https://lore.kernel.org/all/20211011134508.748956131%40linuxfoundation.org/
https://www.debian.org/security/2022/dsa-5096

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