Read the docs
TI-2021-09212 Aliases CVE-2021-27854GHSA-433g-q37h-7crr

L2 network filtering bypass using stacked VLAN0, LLC/SNAP headers, and Ethernet to Wifi frame translation

Priority LOW 23CWE-290Published · Updated

Key facts

Attack vector
Adjacent network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
None · Low · None
Fix status
No fix listed

Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA. Impact type from CWE-290.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00714 53rd percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
IETFP802.1QD1.0 – D1.0—No fix listedCNA
IETFdraft-ietf-v6ops-ra-guard08 – 08—No fix listedCNA
IEEE802.2802.2h-1997 – 802.2h-1997—No fix listedCNA
  • P802.1Q VendorIETF Affected D1.0 – D1.0 Fixed in — No fix listed CNA
  • draft-ietf-v6ops-ra-guard VendorIETF Affected 08 – 08 Fixed in — No fix listed CNA
  • 802.2 VendorIEEE Affected 802.2h-1997 – 802.2h-1997 Fixed in — No fix listed CNA

CPE configurations NVD · 2

CPEVersionsRoleVendor
cpe:2.3:a:ieee:ieee_802.2:*:*:*:*:*:*:*:*up to 802.2h-1997VulnerableIEEE
cpe:2.3:a:ietf:p802.1q:*:*:*:*:*:*:*:*up to d1.0VulnerableIETF
  • cpe:2.3:a:ieee:ieee_802.2:*:*:*:*:*:*:*:* Versions up to 802.2h-1997 Vulnerable ·IEEE
  • cpe:2.3:a:ietf:p802.1q:*:*:*:*:*:*:*:* Versions up to d1.0 Vulnerable ·IETF

Remediation

No fixed version listed by the sources yet.

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Not affected: 4 products
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 9

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-27854
  2. 2026-10-03 Alias added: GHSA-433g-q37h-7crr

References

Advisory 3

Other 2

  • TI-2021-09220 Authentication bypass by spoofing in IEEE 802.2 CVSS 3.1MEDIUM 4.7
  • TI-2021-09219 L2 network filtering bypass using stacked VLAN0 and LLC/SNAP headers with invalid lengths CVSS 3.1MEDIUM 4.7
  • TI-2021-09211 L2 network filtering can be bypassed using stacked VLAN0 and LLC/SNAP headers CVSS 3.1MEDIUM 4.7

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences