CVE-2021-27853

MEDIUM

IEEE 802.2 < 802.2h-1997 - Authentication Bypass via VLAN 0 and LLC/SNAP Header Spoofing

Title source: llm
STIX 2.1

Description

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.

References (7)

Core 7
Core References
Exploit, Third Party Advisory
https://blog.champtar.fr/VLAN0_LLC_SNAP/
Technical Description, Third Party Advisory
https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/
Third Party Advisory, US Government Resource
https://kb.cert.org/vuls/id/855201
Third Party Advisory, US Government Resource
https://www.kb.cert.org/vuls/id/855201

Scores

CVSS v3 4.7
EPSS 0.0011
EPSS Percentile 28.7%
Attack Vector ADJACENT_NETWORK
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact partial

Details

CWE
CWE-290
Status published
Products (50)
cisco/catalyst_6503-e_firmware 15.5\(01.01.85\)sy07
cisco/catalyst_6504-e_firmware 15.5\(01.01.85\)sy07
cisco/catalyst_6506-e_firmware 15.5\(01.01.85\)sy07
cisco/catalyst_6509-e_firmware 15.5\(01.01.85\)sy07
cisco/catalyst_6509-neb-a_firmware 15.5\(01.01.85\)sy07
cisco/catalyst_6509-v-e_firmware 15.5\(01.01.85\)sy07
cisco/catalyst_6513-e_firmware 15.5\(01.01.85\)sy07
cisco/catalyst_6800ia_firmware 15.5\(01.01.85\)sy07
cisco/catalyst_6807-xl_firmware 15.5\(01.01.85\)sy07
cisco/catalyst_6840-x_firmware 15.5\(01.01.85\)sy07
... and 40 more
Published Sep 27, 2022
Tracked Since Feb 18, 2026