VulnerabilityModified
CVE-2021-27853
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.
MEDIUM 4.7EPSS 0.81%
Does this matter?
Lower severity and a low EPSS score (0.81%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 4.7 MEDIUMCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
- EPSS
- 0.81% probability · 57th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- 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 · +40 more
- Source
- cret@cert.org
EPSS 0.8% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://blog.champtar.fr/VLAN0_LLC_SNAP/Exploit, Third Party Advisory
- https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/Technical Description, Third Party Advisory
- https://kb.cert.org/vuls/id/855201Third Party Advisory, US Government Resource
- https://standards.ieee.org/ieee/802.1Q/10323/Vendor Advisory
- https://standards.ieee.org/ieee/802.2/1048/Vendor Advisory
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTXThird Party Advisory
- https://blog.champtar.fr/VLAN0_LLC_SNAP/Exploit, Third Party Advisory
- https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/Technical Description, Third Party Advisory
- https://kb.cert.org/vuls/id/855201Third Party Advisory, US Government Resource
- https://standards.ieee.org/ieee/802.1Q/10323/Vendor Advisory
- https://standards.ieee.org/ieee/802.2/1048/Vendor Advisory
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTXThird Party Advisory
- https://www.kb.cert.org/vuls/id/855201
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.