Jason Geffner of CrowdStrike has discovered a security vulnerability that affects several virtual machine platforms, including Xen, KVM, VirtualBox, and QEMU. Taking advantage of a bug in Floppy Disk Controller code that has existed since 2004, this flaw may allow “…attackers to escape from the confines of an affected virtual machine (VM) guest and potentially obtain code-execution access to the host.” This flaw is operating system agnostic, meaning it affects all host platforms running the VM software (including but not limited to Linux, Windows, and Mac OS X.)
Once an attacker has reached the host, they can attack it or other VMs hosted on the affected machine. The VENOM (Virtualized Environment Neglected Operations Manipulation) website prepared by CrowdStrike illustrates how the flaw can affect a system. VENOM has been classified as CVE-215-3456 in the US National Vulnerability Database. According to the report, the following hypervisors are NOT affected: VMware, Microsoft Hyper-V, and Bochs.
In order for an attacker to benefit from VENOM, they would require administrative/root privileges on their guest operating system. To date, no exploits utilizing VENOM have been seen in the wild, but this does not mean that none exist. The VENOM site describes the vulnerability as follows:
“The guest operating system communicates with the FDC [floppy disk controller] by sending commands such as seek, read, write, format, etc. to the FDC’s input/output port. QEMU’s virtual FDC uses a fixed-size buffer for storing these commands and their associated data parameters. The FDC keeps track of how much data to expect for each command and, after all expected data for a given command is received from the guest system, the FDC executes the command and clears the buffer for the next command.
This buffer reset is performed immediately at the completion of processing for all FDC commands, except for two of the defined commands. An attacker can send these commands and specially crafted parameter data from the guest system to the FDC to overflow the data buffer and execute arbitrary code in the context of the host’s hypervisor process.”
Administrators are cautioned that just because they do not actively use their virtual drive does not mean they are immune to attack. Floppy drives are added by default to new virtual machines by default, and “an unrelated bug causes the vulnerable FDC code to remain active and exploitable by attackers.” (Emphasis added.)
[5-21-2015 - Minor title change to reflect vulnerability rather than exploit]