CVE-2021-27854

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.

CVSS v3 4.7 MEDIUM

4.7^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 1.4

Attack Vector ADJACENT_NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact NONE

Scope CHANGED

References

Link	Resource
https://blog.champtar.fr/VLAN0_LLC_SNAP/
https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/	Vendor Advisory
https://kb.cert.org/vuls/id/855201
https://standards.ieee.org/ieee/802.1Q/10323/	Vendor Advisory
https://standards.ieee.org/ieee/802.2/1048/	Vendor Advisory
https://blog.champtar.fr/VLAN0_LLC_SNAP/
https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/	Vendor Advisory
https://kb.cert.org/vuls/id/855201
https://standards.ieee.org/ieee/802.1Q/10323/	Vendor Advisory
https://standards.ieee.org/ieee/802.2/1048/	Vendor Advisory
https://www.kb.cert.org/vuls/id/855201

Configurations

Configuration 1 (hide)

cpe:2.3:a:ieee:ieee_802.2:*:*:*:*:*:*:*:*

Configuration 2 (hide)

cpe:2.3:a:ietf:p802.1q:*:*:*:*:*:*:*:*

History

04 Nov 2025, 20:15

Type	Values Removed	Values Added
References		() https://www.kb.cert.org/vuls/id/855201 -

21 Nov 2024, 05:58

Type	Values Removed	Values Added
References	~~() https://blog.champtar.fr/VLAN0_LLC_SNAP/ -~~	() https://blog.champtar.fr/VLAN0_LLC_SNAP/ -
References	~~() https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/ - Vendor Advisory~~	() https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/ - Vendor Advisory
References	~~() https://kb.cert.org/vuls/id/855201 -~~	() https://kb.cert.org/vuls/id/855201 -
References	~~() https://standards.ieee.org/ieee/802.1Q/10323/ - Vendor Advisory~~	() https://standards.ieee.org/ieee/802.1Q/10323/ - Vendor Advisory
References	~~() https://standards.ieee.org/ieee/802.2/1048/ - Vendor Advisory~~	() https://standards.ieee.org/ieee/802.2/1048/ - Vendor Advisory

Information

Published : 2022-09-27 19:15

Updated : 2025-11-04 20:15

NVD link : CVE-2021-27854

Mitre link : CVE-2021-27854

CVE.ORG link : CVE-2021-27854

JSON object : View

Products Affected

ietf

p802.1q

ieee

ieee_802.2

CWE

CWE-290

Authentication Bypass by Spoofing

{"id": "CVE-2021-27854", "cveTags": [], "metrics": {"cvssMetricV31": [{"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "CHANGED", "version": "3.1", "baseScore": 4.7, "attackVector": "ADJACENT_NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "NONE"}, "impactScore": 1.4, "exploitabilityScore": 2.8}, {"type": "Secondary", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "cvssData": {"scope": "CHANGED", "version": "3.1", "baseScore": 4.7, "attackVector": "ADJACENT_NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "NONE"}, "impactScore": 1.4, "exploitabilityScore": 2.8}]}, "published": "2022-09-27T19:15:09.240", "references": [{"url": "https://blog.champtar.fr/VLAN0_LLC_SNAP/", "source": "cret@cert.org"}, {"url": "https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/", "tags": ["Vendor Advisory"], "source": "cret@cert.org"}, {"url": "https://kb.cert.org/vuls/id/855201", "source": "cret@cert.org"}, {"url": "https://standards.ieee.org/ieee/802.1Q/10323/", "tags": ["Vendor Advisory"], "source": "cret@cert.org"}, {"url": "https://standards.ieee.org/ieee/802.2/1048/", "tags": ["Vendor Advisory"], "source": "cret@cert.org"}, {"url": "https://blog.champtar.fr/VLAN0_LLC_SNAP/", "source": "af854a3a-2127-422b-91ae-364da2661108"}, {"url": "https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/", "tags": ["Vendor Advisory"], "source": "af854a3a-2127-422b-91ae-364da2661108"}, {"url": "https://kb.cert.org/vuls/id/855201", "source": "af854a3a-2127-422b-91ae-364da2661108"}, {"url": "https://standards.ieee.org/ieee/802.1Q/10323/", "tags": ["Vendor Advisory"], "source": "af854a3a-2127-422b-91ae-364da2661108"}, {"url": "https://standards.ieee.org/ieee/802.2/1048/", "tags": ["Vendor Advisory"], "source": "af854a3a-2127-422b-91ae-364da2661108"}, {"url": "https://www.kb.cert.org/vuls/id/855201", "source": "af854a3a-2127-422b-91ae-364da2661108"}], "vulnStatus": "Modified", "weaknesses": [{"type": "Secondary", "source": "cret@cert.org", "description": [{"lang": "en", "value": "CWE-290"}]}, {"type": "Primary", "source": "nvd@nist.gov", "description": [{"lang": "en", "value": "CWE-290"}]}], "descriptions": [{"lang": "en", "value": "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."}, {"lang": "es", "value": "Las capacidades de filtrado de red de capa 2, como la protecci\u00f3n RA de IPv6, pueden omitirse usando combinaciones de encabezados VLAN 0, encabezados LLC/SNAP y convirtiendo tramas de Ethernet a Wifi y su inversa"}], "lastModified": "2025-11-04T20:15:59.750", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:ieee:ieee_802.2:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "D5B0DDC2-21C5-4682-9AA2-055BF7C722DA", "versionEndIncluding": "802.2h-1997"}], "operator": "OR"}]}, {"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:ietf:p802.1q:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "94105D2E-950F-4290-8840-301FA908BC8C", "versionEndIncluding": "d1.0"}], "operator": "OR"}]}], "sourceIdentifier": "cret@cert.org"}