CVE-2021-27853

moderate-risk
Published 2022-09-27

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.

Do I need to act?

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0.15% chance of exploitation
EPSS score — low exploit probability
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Not on CISA KEV list
No confirmed active exploitation reported to CISA
?
Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
4
CVSS 4.7/10 Medium
ADJACENT_NETWORK / LOW complexity

Affected Products (20)

Ieee 802.2
P802.1Q
Catalyst 6503-E Firmware
Catalyst 6504-E Firmware
Catalyst 6506-E Firmware
Catalyst 6509-E Firmware
Catalyst 6509-Neb-A Firmware
Catalyst 6509-V-E Firmware
Catalyst 6513-E Firmware
Catalyst 6807-Xl Firmware
Catalyst 6840-X Firmware
Catalyst 6880-X Firmware
Catalyst C6816-X-Le Firmware
Catalyst C6824-X-Le-40G Firmware
Catalyst C6832-X-Le Firmware
Catalyst C6840-X-Le-40G Firmware
Catalyst 6800Ia Firmware

Affected Vendors

Cisco Ieee Ietf

References (13)

Exploit https://blog.champtar.fr/VLAN0_LLC_SNAP/
Technical Description https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/
Third Party Advisory https://kb.cert.org/vuls/id/855201
Vendor Advisory https://standards.ieee.org/ieee/802.1Q/10323/
Vendor Advisory https://standards.ieee.org/ieee/802.2/1048/
Third Party Advisory https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-V...
Exploit https://blog.champtar.fr/VLAN0_LLC_SNAP/
Technical Description https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/
Third Party Advisory https://kb.cert.org/vuls/id/855201
Vendor Advisory https://standards.ieee.org/ieee/802.1Q/10323/
Vendor Advisory https://standards.ieee.org/ieee/802.2/1048/
Third Party Advisory https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-V...
https://www.kb.cert.org/vuls/id/855201
47
/ 100
moderate-risk
Severity 16/34 · Moderate
Exploitability 1/34 · Minimal
Exposure 30/34 · Critical