CVE-2021-27853

Public Exploit
L2 network filtering can be bypassed using stacked VLAN0 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.

Category

4.7
CVSS
Severity: Medium
CVSS 3.1 •
EPSS 0.02%
Vendor Advisory cisco.com Vendor Advisory ieee.org Vendor Advisory ieee.org
Affected: IEEE 802.2
Affected: IETF draft-ietf-v6ops-ra-guard
Affected: IETF P802.1Q
Published at:
Updated at:

References

Link Tags
https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/ third party advisory technical description
https://standards.ieee.org/ieee/802.2/1048/ vendor advisory
https://standards.ieee.org/ieee/802.1Q/10323/ vendor advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTX third party advisory vendor advisory
https://kb.cert.org/vuls/id/855201 third party advisory us government resource
https://blog.champtar.fr/VLAN0_LLC_SNAP/ third party advisory exploit

Frequently Asked Questions

What is the severity of CVE-2021-27853?
CVE-2021-27853 has been scored as a medium severity vulnerability.
How to fix CVE-2021-27853?
To fix CVE-2021-27853, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2021-27853 being actively exploited in the wild?
It is possible that CVE-2021-27853 is being exploited or will be exploited in a near future based on public information. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-27853?
CVE-2021-27853 affects IEEE 802.2, IETF draft-ietf-v6ops-ra-guard, IETF P802.1Q.
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