CVE Tools
Sign in

CVE-2021-27861

L2 network filtering bypass using stacked VLAN0 and LLC/SNAP headers with invalid lengths

Published: Sep 27, 2022Updated: Nov 4, 2025 Sources: CVE List NVDCWE-130
NVD MITRE
4.7CVSSMEDIUM
EPSS Score
0.6%
Top 57.0%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
No Fix Available

Description

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

CVSS Vector Breakdown

AV:AAC:LPR:NUI:NS:CC:NI:LA:N
Exploitability
AV:AAttack Vector
Adjacent
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:CScope
Changed
Impact
C:NConfidentiality
None
I:LIntegrity
Low
A:NAvailability
None
Open in CVSS calculator →

Weaknesses

CWE-130CWE-290

Affected Products

ieee 802.2ieee
p802.1qietf
802.2IEEE
draft-ietf-v6ops-ra-guardIETF
P802.1QIETF

Attack Graph

Products CVE Techniques Tactics

Click technique nodes to view MITRE ATT&CK details. Scroll to zoom, drag to pan.

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

MITRE ATT&CK

1 technique
Initial Access
View detailed technique mapping

References

https://blog.champtar.fr/VLAN0_LLC_SNAP/
blog.champtar.fr
https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/
datatracker.ietf.org
https://kb.cert.org/vuls/id/855201
kb.cert.org
and 3 more references View all →

Timeline

Published
Sep 27, 2022
Last Updated
Nov 4, 2025

Unlock Complete Vulnerability Intelligence

Get the full picture for CVE-2021-27861 and every CVE in our database. Create a free account — no credit card required.

Create Free Account
Plain-language analysis
Impact assessment and exploitation scenario in plain English
Attack graph visualization
Interactive attack path and kill chain mapping
Exploit details & PoC links
ExploitDB, Metasploit, GitHub PoCs with direct links
Nuclei scanner templates
Ready-to-use vulnerability scanner templates
Full remediation guide
Patch instructions, workarounds, and compliance impact
Interactive AI chat
Ask questions about this vulnerability in natural language
Related vulnerabilities
Semantically similar CVEs and attack patterns
REST API & MCP access
Integrate vulnerability data into your workflows