On September 27, 2022, the following vulnerabilities affecting Cisco products were disclosed by Cert/CC as part of VU855201, titled L2 network security controls can be bypassed using VLAN 0 stacking and/or 802.3 headers:
CVE-2021-27853: Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed using a combination of VLAN 0 headers and LLC/SNAP headers.
CVE-2021-27854: Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using a combination of VLAN 0 headers, LLC/SNAP headers in Ethernet to Wifi frame translation, and in the reverse—Wifi to Ethernet.
CVE-2021-27861: Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length (and optionally VLAN0 headers).
CVE-2021-27862: Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length and Ethernet to Wifi frame conversion (and optionally VLAN0 headers).
Exploitation of these vulnerabilities…
