What is CVE-2021-3635?

CVE-2021-3635 is a medium-severity vulnerability in Linux Kernel, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 4.4/10. Published 2021-08-13.

How severe is CVE-2021-3635?

Medium severity. CVSS v3 base score is 4.4 out of 10.

Buffer overflow in Linux Kernel

CVE-2021-3635

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.

Vulnerability class: Buffer Overflow

Published 2021-08-13 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 4.4 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.002 (14.5th percentile), scored 2026-10-02.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 14.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000

Affected products

Linux Kernel — versions 5.5
Fedoraproject Fedora — versions 34
Red Hat Enterprise Linux — versions 6.0, 7.0, 8.0
Kernel — versions kernel 5.5-rc7

Weakness classification (CWE)

CWE-119 — Improper Restriction of Operations within the Bounds of a Memory Buffer

References

bugzilla.redhat.com/show_bug.cgi (Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-3635?: CVE-2021-3635 is a medium-severity vulnerability in Linux Kernel, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 4.4/10. Published 2021-08-13.
How severe is CVE-2021-3635?: Medium severity. CVSS v3 base score is 4.4 out of 10.