From: giuseppe.citerna@tin.it
Date: Sun Aug 07 2005 - 04:42:14 GMT-3
Hello, i have read many doc about this exploit but there are any contradictions.
I hnow that this exploit exist in 3 ways :
1) Basic=> The attacker spoof a switch and gains the trunked states of the switch's port. Rely on auto-negotiate feature turned ON. This ways is simple to understand and to block
2) Complex 1 => This attack is described on http://www.sans.org/resources/idfaq/vlan.php and to work need that the attacker and the trunk share same native vlan ( ex. VLAN 10 ). In this
doc. the attacker send on the access port ( VLAN 10 ) a tagged frame with a VLAN-ID of target VLAN ( ex. VLAN 20 ) . The switch takes frame and forward it on trunk port without native tag (10). The other switch (connected via-trunk) read VLAN-ID(20) and forward frame on the access vlan 20.
In this scenario my doubts is :
- Why the first SW accepts tagged frame ?
Is this behavior an anomaly of work ?
- Why the last switch that receives native frame on trunk port reads the VLAN-ID ? Is this normal or anomaly ? I think that sw does'nt read VLAN-ID because the frame on trunk is native .
2)Complex 2 => In other docs per ex: http://www.cisco.com/en/US/products/hw/switches/ps708/products_white_... there is an attack called " Double-Encapsulated 802.1Q ". In this
exploit the conditions are similar to the
precedent but the attacker need to insert two VLAN-ID ( outer,inner ). If this case work then the first switch read VLAN-ID on access port and forward frame on trunk ( strip off first VLAN-ID ) . This behavior is different that
precedent case . Why the switch forward this frame according to VLAN-ID
on the access-port ? Is this behavior another anomalies ?
Sorry about lenght of post but i want to understand if this vulnerability were resolved or not .
Thanks
Giuseppe Citerna
ccie#10503
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