CVE-2021-27861

CVE-2021-27861 describes a vulnerability allowing bypass of Layer 2 network filtering, specifically IPv6 RA guard, through the use of LLC/SNAP headers with invalid lengths, optionally combined with VLAN0 headers. This medium-severity vulnerability (CVSS 4.7, AV:A/AC:L) affects IEEE 802.2 and 802.1Q implementations, enabling potential denial-of-service or man-in-the-middle attacks within an adjacent network. While there is no known active exploitation or public exploit code (Metasploit, Nuclei, ExploitDB), the vulnerability has garnered significant community discussion and media coverage, indicating awareness within the cybersecurity landscape.