{"schema_version":"public-product-v1.1","generated_at":"2026-07-21T11:17:08Z","exposure_verdict":"not_assessed","verdict_reason":"Public evidence does not evaluate exact release, platform, enabled features, configuration, compensating controls, or live exposure.","advisory":{"id":"cisco-sa-VU855201-J3z8CKTX","slug":"cisco-sa-vu855201-j3z8cktx","vendor":"Cisco","title":"Vulnerabilities in Layer 2 Network Security Controls Affecting Cisco Products: September 2022","summary":"On September 27, 2022, the following vulnerabilities affecting Cisco products were disclosed by Cert/CC as part of VU855201, titled L2 network security controls can be bypassed using VLAN 0 stacking and/or 802.3 headers: CVE-2021-27853: Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed using a combination of VLAN 0 headers and LLC/SNAP headers. CVE-2021-27854: Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using a combination of VLAN 0 headers, LLC/SNAP headers in Ethernet to Wifi frame translation, and in the reverse—Wifi to Ethernet. CVE-2021-27861: Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length (and optionally VLAN0 headers). CVE-2021-27862: Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length and Ethernet to Wifi frame conversion (and optionally VLAN0 headers). Exploitation of these vulnerabilities could allow an adjacent attacker to bypass configured first-hop security (FHS) features on the affected Cisco products. For more information about these vulnerabilities, see the Details section of this advisory. This advisory is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTX","severity":"Medium","published_at":"2022-09-27T16:00:00Z","updated_at":"2022-10-05T18:16:08Z","source_url":"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTX","csaf_url":"https://sec.cloudapps.cisco.com/security/center/contentjson/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTX/csaf/cisco-sa-VU855201-J3z8CKTX.json","exposure_verdict":"not_assessed","verdict_reason":"Public evidence does not evaluate exact release, platform, enabled features, configuration, compensating controls, or live exposure."},"freshness":{"last_source_refreshed_at":"2026-07-21T05:16:34Z","latest_source_refresh_at":"2026-07-21T05:16:34Z","oldest_source_refresh_at":"2026-07-21T03:00:03Z","all_sources_fresh":true,"sources":[{"source":"cisco_advisories","label":"Cisco 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