CVE-2021-3635

Severity: medium (CVSS 4.4 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: 2021-08-13 · updated 2026-06-17
Weakness: CWE-119

Description

A flaw was found in the Linux kernel netfilter implementation in versions prior to 5.5-rc7. A user with root (CAP_SYS_ADMIN) access is able to panic the system when issuing netfilter netflow commands.

Affected products

Fedoraproject Fedora: 34
Linux kernel: before 5.5; 5.5-rc1, 5.5-rc2, 5.5-rc3, 5.5-rc4, 5.5-rc5, 5.5-rc6 — fixed in 5.5
Red Hat Enterprise Linux: 6.0, 7.0, 8.0

How to fix

Upgrade to a fixed version: Linux kernel 5.5. Check the vendor advisory for mitigations.

References

https://bugzilla.redhat.com/show_bug.cgi?id=1976946
https://bugzilla.redhat.com/show_bug.cgi?id=1976946

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