Xen's highly critical virtual machine escape flaw gets a fix

It's possibly the worst flaw ever found in the Xen hypervisor, researchers say

The Xen Project fixed several vulnerabilities in its popular virtualization software, including one that could allow potential attackers to break out of a virtual machine and gain control over the host system.

Vulnerabilities that break the isolation layer between virtual machines are the most serious type for a hypervisor like Xen, whose main goal is to allow running multiple VMs on the same hardware in a secure manner.

The Xen patches released Thursday fix a total of nine vulnerabilities, but the privilege escalation one identified as CVE-2015-7835 is the most serious one.

It stems not from a traditional programming error, but from a logic flaw in how Xen implements memory virtualization for PV (paravirtualized) VMs. PV is a technique that enables virtualization on CPUs that don't support hardware-assisted virtualization.

As such, the flaw can only be exploited by malicious administrators of PV guests and only on x86 systems, the Xen Project said in an advisory. Xen versions 3.4 and higher are vulnerable.

The vulnerability, which has existed for 7 years, is "probably the worst we have seen affecting the Xen hypervisor, ever," the security team of the Qubes OS Project said in its own advisory. Qubes OS relies on Xen to compartmentalize different tasks performed by users for increased security.

"It is really shocking that such a bug has been lurking in the core of the hypervisor for so many years," the Qubes security team said. "In our opinion the Xen project should rethink their coding guidelines and try to come up with practices and perhaps additional mechanisms that would not let similar flaws to plague the hypervisor ever again (assert-like mechanisms perhaps?). Otherwise the whole project makes no sense, at least to those who would like to use Xen for security-sensitive work."

Join the newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.
Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.
Lucian Constantin

Lucian Constantin

IDG News Service
Show Comments

Brand Post

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Tom Pope

Dynabook Portégé X30L-G

Ultimately this laptop has achieved everything I would hope for in a laptop for work, while fitting that into a form factor and weight that is remarkable.

Tom Sellers

MSI P65

This smart laptop was enjoyable to use and great to work on – creating content was super simple.

Lolita Wang

MSI GT76

It really doesn’t get more “gaming laptop” than this.

Jack Jeffries

MSI GS75

As the Maserati or BMW of laptops, it would fit perfectly in the hands of a professional needing firepower under the hood, sophistication and class on the surface, and gaming prowess (sports mode if you will) in between.

Taylor Carr

MSI PS63

The MSI PS63 is an amazing laptop and I would definitely consider buying one in the future.

Christopher Low

Brother RJ-4230B

This small mobile printer is exactly what I need for invoicing and other jobs such as sending fellow tradesman details or step-by-step instructions that I can easily print off from my phone or the Web.

Featured Content

Product Launch Showcase

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?