Virtual network isolation: Are we there yet?

While multi-tenant cloud computing provides great benefits in terms of resource sharing, it introduces a new security landscape and requires strong network isolation guarantees between the tenants. Such network isolation is typically implemented using network virtualization: Virtual switches residing in the virtualization layer enforce isolation, e.g., via tunnel protocols and per-tenant flow rules. The design of such switches is a very active topic: Since 2009 alone, at least 22 different designs have been introduced. Our systematic analysis of 22 virtual switches uncovers 4 security weaknesses: Colocation, single point of failure, privileged packet processing and manual packet parsing. An attacker can easily undermine network isolation by exploiting those weaknesses. Hence, we introduce 3 secure design principles to build a resilient virtual switch, thereby offering strong virtual network isolation.