There's an extremely critical bug in the Xen, KVM, and native QEMU virtual machine platforms and appliances that makes it possible for attackers to break out of protected guest environments and take full control of the operating system hosting it, security researchers warned Wednesday.
The vulnerability is serious because it pierces a key protection that many cloud service providers use to segregate one customer's data from another. If attackers with access to one virtualized environment can escape to the underlying operating system, they could potentially access all other virtual environments. In the process, they would be undermining one of the fundamental guarantees of virtual machines. Compounding the severity, the vulnerability resides in a low-level disk controller, allowing it to be exploited when guest or host OSes alike run Linux, Windows, Mac OS X, or possibly other OSes. Researchers from security firm CrowdStrike, who first warned of the vulnerability, wrote:
Most VM escape vulnerabilities discovered in the past were only exploitable in non-default configurations or in configurations that wouldn’t be used in secured environments. Other VM escape vulnerabilities only applied to a single virtualization platform, or didn’t directly allow for arbitrary code execution.
- CVE-2007-1744 – Directory traversal vulnerability in shared folders feature
- CVE-2008-0923 – Path traversal vulnerability in VMware’s shared folders implementation
- CVE-2009-1244 – Cloudburst (VMware virtual video adapter vulnerability)
- CVE-2012-0217 – 64-bit PV guest privilege escalation vulnerability
- CVE-2014-0983 – Oracle VirtualBox 3D acceleration multiple memory corruption vulnerabilities
VENOM (CVE-2015-3456) is unique in that it applies to a wide array of virtualization platforms, works on default configurations, and allows for direct arbitrary code execution.
The vulnerability is the result of a buffer-overflow bug in QEMU's virtual Floppy Disk Controller, which is used in a variety of virtualization platforms and appliances. It is known to affect Xen, KVM, and the native QEMU client software, and it may affect others. VMware, Microsoft Hyper-V, and Bochs hypervisors are not affected. At publication time, patches were available from the Xen Project and the QEMU Project. There are also workarounds users can follow to lessen the risk of exploitation. The vulnerability is serious enough that users of other virtualization packages should immediately contact the developers to find out if they're susceptible.