Mathias Payer

Modern systems rely on Address-Space Layout Ran-domization (ASLR) and Data Execution Prevention (DEP) to protect software against memory corruption vulnera-bilities. The security of ASLR depends on randomizing regions in memory which can be broken by leaking ad-dresses. While information leaks are common for client applications, server software has been hardened to reduce such information leaks. Memory deduplication is a common feature of Virtual Machine Monitors (VMMs) that reduces the memory footprint and increases the cost-effectiveness of virtual machines (VMs) running on the same host. Memory pages with the same content are merged into one read-only memory page. Writing to these pages is expensive due to page faults caused by the memory protection, and this cost can be used by an attacker as a side-channel to detect whether a page has been shared. Leveraging this memory side-channel, we craft an attack that leaks the address-space layouts of the neighboring VMs, and hence, defeats ASLR. Our proof-of-concept exploit, CAIN (Cross-VM ASL INtrospection) defeats ASLR of a 64-bit Windows Server 2012 victim VM in less than 5 hours (for 64-bit Linux victims the attack takes several days). Further, we show that CAIN reliably defeats ASLR, regardless of the number of victim VMs or the system load.