{"id":"CVE-2021-27853","url":"https://www.cyber-defence.io/tools/cve/CVE-2021-27853","generatedAt":"2026-10-27T22:28:22.977Z","title":"Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed using combinations of VLAN 0 headers and LLC/SNAP headers.","description":"Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed using combinations of VLAN 0 headers and LLC/SNAP headers.","published":"2022-09-27T18:15:10.000Z","lastModified":"2026-06-17T03:45:31.000Z","status":"Modified","sourceIdentifier":"cret@cert.org","cvss":{"version":"3.1","score":4.7,"severity":"MEDIUM","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N"},"cwe":["CWE-290"],"affected":["ieee/ieee 802.2","ietf/p802.1q","cisco/catalyst 6503-e firmware","cisco/catalyst 6504-e firmware","cisco/catalyst 6506-e firmware","cisco/catalyst 6509-e firmware","cisco/catalyst 6509-neb-a firmware","cisco/catalyst 6509-v-e firmware","cisco/catalyst 6513-e firmware","cisco/catalyst 6807-xl firmware","cisco/catalyst 6840-x firmware","cisco/catalyst 6880-x firmware","cisco/catalyst c6816-x-le firmware","cisco/catalyst c6824-x-le-40g firmware","cisco/catalyst c6832-x-le firmware","cisco/catalyst c6840-x-le-40g firmware","cisco/catalyst 6800ia firmware","cisco/ios xe","cisco/meraki ms390 firmware","cisco/meraki ms210 firmware","cisco/meraki ms225 firmware","cisco/meraki ms250 firmware","cisco/meraki ms350 firmware","cisco/meraki ms355 firmware","cisco/meraki ms410 firmware","cisco/meraki ms420 firmware","cisco/meraki ms425 firmware","cisco/meraki ms450 firmware","cisco/nexus 93180yc-ex firmware","cisco/nexus 93180yc-fx firmware","cisco/nexus 93180yc-fx3 firmware","cisco/nexus 93240yc-fx2 firmware","cisco/nexus 93360yc-fx2 firmware","cisco/nexus 93120tx firmware","cisco/nexus 93108tc-ex firmware","cisco/nexus 9348gc-fxp firmware","cisco/nexus 93108tc-fx firmware","cisco/nexus 93108tc-fx3p firmware","cisco/nexus 93216tc-fx2 firmware","cisco/n9k-c9316d-gx firmware","cisco/n9k-c93600cd-gx firmware","cisco/n9k-c9332d-gx2b firmware","cisco/n9k-c9348d-gx2a firmware","cisco/n9k-c9364d-gx2a firmware","cisco/n9k-x97160yc-ex firmware","cisco/n9k-x9788tc-fx firmware","cisco/n9k-x9564px firmware","cisco/n9k-x9464px firmware","cisco/n9k-x9564tx firmware","cisco/n9k-x9464tx2 firmware","cisco/nexus 9636pq firmware","cisco/nexus x9636q-r firmware","cisco/nexus 9536pq firmware","cisco/nexus 9432pq firmware","cisco/nexus 9736pq firmware","cisco/n9k-x9736c-fx firmware","cisco/n9k-x9732c-ex firmware","cisco/n9k-x9732c-fx firmware","cisco/n9k-x9736c-ex firmware","cisco/n9k-x9636c-rx firmware"],"epss":{"score":0.00813,"percentile":0.5673,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (0.81%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://blog.champtar.fr/VLAN0_LLC_SNAP/","tags":["Exploit","Third Party Advisory"],"source":"cret@cert.org"},{"url":"https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/","tags":["Technical Description","Third Party Advisory"],"source":"cret@cert.org"},{"url":"https://kb.cert.org/vuls/id/855201","tags":["Third Party Advisory","US Government Resource"],"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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTX","tags":["Third Party Advisory"],"source":"cret@cert.org"},{"url":"https://blog.champtar.fr/VLAN0_LLC_SNAP/","tags":["Exploit","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/","tags":["Technical Description","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://kb.cert.org/vuls/id/855201","tags":["Third Party Advisory","US Government Resource"],"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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTX","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.kb.cert.org/vuls/id/855201","source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2021-27853","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}