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IEEE 802.1q Unauthorized VLAN Traversal Weakness

The 802.1q standard is susceptible to issues that allow attackers to send and receive packets from one VLAN to another without authorization.

By spoofing various Ethernet frame fields such as the source or destination MAC addresses, IP addresses, and VLAN tags, attackers may cause packets to traverse from one VLAN to another, and possibly back again. Attackers may also add multiple VLAN tags to packets to cause multiple routers to decapsulate the packets in unexpected ways, aiding the attacker in traversing VLANs.

This issue allows attackers to traverse from one VLAN to another in an unauthorized fashion. As some users may utilize VLANs to segregate network segments containing differing security properties, this may have various consequences.

This issue may be exacerbated by utilizing attacker-controlled external network hosts to bounce packets between VLANs.