Home/CVE/Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length
CVE

CVE-2021-27861

Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length

Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length (and optionally VLAN0 headers)

MEDIUM · CVSS 4.7 EPSS 0.00111
Monitor
  • No active-exploitation, high-EPSS, or public-exploit signals - routine patching cadence
Sigma rules0 YARA rules0
⬡

Weakness Classification

CWE-130Improper Handling of Length Parameter Inconsistency
CWE-290Authentication Bypass by Spoofing
CWE-290Authentication Bypass by Spoofing
▤

Affected Products & Versions

2
ieee 802.2<= 802.2h-1997
ietf p802.1q<= d1.0
▣

Scoring & Timeline

4.7
MEDIUM · CVSS v3.1 · cret@cert.org
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD27 Sep 2022 · 07:15 PM
CVSS VectorCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
no
Technical impact
partial
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
⚑

Vendor Advisories

1
cisco-csafcisco-sa-VU855201-J3z8CKTX
🔗

References & Sources

6
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://blog.champtar.fr/VLAN0_LLC_SNAP/
https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/Third Party Advisory
https://kb.cert.org/vuls/id/855201
https://standards.ieee.org/ieee/802.1Q/10323/Third Party Advisory
https://standards.ieee.org/ieee/802.2/1048/Third Party Advisory
https://www.kb.cert.org/vuls/id/855201
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