What is CVE-2021-27854?

CVE-2021-27854 is a medium-severity vulnerability in Ieee 802.2, classified under Authentication Bypass by Spoofing. CVSS score: 4.7/10. Published 2022-09-27.

How severe is CVE-2021-27854?

Medium severity. CVSS v3 base score is 4.7 out of 10.

Vulnerability in Ieee 802.2

CVE-2021-27854

Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using combinations of VLAN 0 headers, LLC/SNAP headers, and converting frames from Ethernet to Wifi and its reverse.

Published 2022-09-27 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 4.7 (Medium). Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.007 (51.8th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 52nd percentile — 51.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: +0.000

Affected products

Ieee 802.2 — versions 802.2h-1997
Ieee 802.2
Ietf Draft-Ietf-V6ops-Ra-Guard — versions 08
Ietf P802.1q — versions D1.0

Weakness classification (CWE)

CWE-290 — Authentication Bypass by Spoofing

References

datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/ (Vendor Advisory)
standards.ieee.org/ieee/802.2/1048/ (Vendor Advisory)
standards.ieee.org/ieee/802.1Q/10323/ (Vendor Advisory)
kb.cert.org/vuls/id/855201
blog.champtar.fr/VLAN0_LLC_SNAP/
af854a3a-2127-422b-91ae-364da2661108

Frequently asked questions

What is CVE-2021-27854?: CVE-2021-27854 is a medium-severity vulnerability in Ieee 802.2, classified under Authentication Bypass by Spoofing. CVSS score: 4.7/10. Published 2022-09-27.
How severe is CVE-2021-27854?: Medium severity. CVSS v3 base score is 4.7 out of 10.