What is CVE-2021-27853?

CVE-2021-27853 is a medium-severity vulnerability in Cisco Catalyst 3650-12x48fd-E, classified under Authentication Bypass by Spoofing. CVSS score: 4.7/10. Published 2022-09-27.

How severe is CVE-2021-27853?

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

Vulnerability in Cisco Catalyst 3650-12x48fd-E

CVE-2021-27853

Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed using combinations of VLAN 0 headers and LLC/SNAP headers.

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: 0.008 (57.0th percentile), scored 2026-11-02.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 57th percentile — 57.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-290 — Authentication Bypass by Spoofing

References

datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/ (Technical Description, Third Party Advisory)
standards.ieee.org/ieee/802.2/1048/ (Vendor Advisory)
standards.ieee.org/ieee/802.1Q/10323/ (Vendor Advisory)
tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201… (vendor-advisory, Third Party Advisory)
kb.cert.org/vuls/id/855201 (US Government Resource, Third Party Advisory)
blog.champtar.fr/VLAN0_LLC_SNAP/ (Exploit, Third Party Advisory)
af854a3a-2127-422b-91ae-364da2661108

Frequently asked questions

What is CVE-2021-27853?: CVE-2021-27853 is a medium-severity vulnerability in Cisco Catalyst 3650-12x48fd-E, classified under Authentication Bypass by Spoofing. CVSS score: 4.7/10. Published 2022-09-27.
How severe is CVE-2021-27853?: Medium severity. CVSS v3 base score is 4.7 out of 10.