CVE-2021-27861

L2 network filtering bypass using stacked VLAN0 and LLC/SNAP headers with invalid lengths

Description

Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length (and optionally VLAN0 headers)

Categories

4.7
CVSS
Severity: Medium
CVSS 3.1 •
EPSS 0.01%
Third-Party Advisory ietf.org Third-Party Advisory ieee.org Third-Party 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
https://standards.ieee.org/ieee/802.2/1048/ third party advisory
https://standards.ieee.org/ieee/802.1Q/10323/ third party advisory
https://kb.cert.org/vuls/id/855201
https://blog.champtar.fr/VLAN0_LLC_SNAP/

Frequently Asked Questions

What is the severity of CVE-2021-27861?
CVE-2021-27861 has been scored as a medium severity vulnerability.
How to fix CVE-2021-27861?
To fix CVE-2021-27861, 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-2021-27861 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2021-27861 is being actively exploited. 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-2021-27861?
CVE-2021-27861 affects IEEE 802.2, IETF draft-ietf-v6ops-ra-guard, IETF P802.1Q.
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