A primary security risk in iSCSI SANs is that an attacker might sniff transmitted storage data.

Neither the iSCSI adapter nor the ESXi host iSCSI initiator encrypts the data that it transmits to and from the targets, making the data vulnerable to sniffing attacks. You must therefore take additional measures to prevent attackers from easily seeing iSCSI data.

Allowing your virtual machines to share virtual switches and VLANs with your iSCSI configuration potentially exposes iSCSI traffic to misuse by a virtual machine attacker. To help ensure that intruders cannot listen to iSCSI transmissions, make sure that none of your virtual machines can see the iSCSI storage network.

Protect your system by giving the iSCSI SAN a dedicated virtual switch.

If you use an independent hardware iSCSI adapter, make sure that the iSCSI adapter and ESXi physical network adapter are not inadvertently connected outside the host. Such a connection might result from sharing a switch.

If you use dependent hardware or software iscsi adapter, which uses ESXi networking, configure iSCSI storage through a different virtual switch than the one used by your virtual machines.

You can also configure your iSCSI SAN on its own VLAN to improve performance and security. Placing your iSCSI configuration on a separate VLAN ensures that no devices other than the iSCSI adapter can see transmissions within the iSCSI SAN. With a dedicated VLAN, network congestion from other sources cannot interfere with iSCSI traffic.