Critical VM escape vulnerability impacts business systems, data centers

The flaw, dubbed Venom but tracked as CVE-2015-3456, can allow an attacker to break out from the confines of a virtual machine (VM) and execute code on the host system.

This security boundary is critical in protecting the confidentiality of data in data centers, where virtualization is extensively used to allow different tenants to run servers on the same physical hardware.

The flaw is located in the virtual Floppy Disk Controller (FDC) code from the QEMU open source machine emulator and virtualizer. The code is also used by the Xen, KVM and other virtualization platforms.

The VMware, Microsoft Hyper-V, and Bochs hypervisors are not impacted by the vulnerability, according security firm CrowdStrike, whose senior security researcher, Jason Geffner, found the issue.

There have been other VM escape vulnerabilities discovered over the years, but this one stands apart because it affects multiple virtualization platforms in default configurations and is agnostic to the guest or host operating system.

Attackers do need to have root access on the guest OS in order to exploit the flaw and execute code on the hypervisor. But once this is done, they could gain access to other servers running on the same hypervisor or to the network traffic originating from all virtual machines.

Because of a separate bug, on Xen and QEMU the vulnerable FDC code remains active even if the administrator disables the virtual floppy drive for a virtual machine, CrowdStrike said.

The QEMU and Xen projects released patches to address this vulnerability.

"While I do consider the vulnerability severe and recommend system administrators to apply fixes when available -- especially in environments where potentially untrusted users have access to guests with administrative privileges -- I also find it blown out of proportions," said Carsten Eiram, the chief research officer of vulnerability intelligence firm Risk Based Security, via email.

Having to first obtain root/administrator access on the guest system makes the vulnerability harder to exploit because an external attacker would need to chain the flaw with a different vulnerability for the guest OS, Eiram said. Also, it's worth noting that ARM platforms are not affected, he said.

The security team from Red Hat said in a blog post that while in theory the vulnerability has the potential to be used for code execution, it hasn't seen any working exploit that demonstrates this.

"To be able to break out of a guest OS to a host OS is a rare and powerful ability, and such bugs are uncommon," said Tod Beardsley, research manager at Rapid7, via email. "Given this incentive of interestingness, I would expect to see a public proof of concept exploit appear sooner rather than later."