Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Endpoint

10/30/2015
03:10 PM
Connect Directly
Twitter
LinkedIn
RSS
E-Mail
50%
50%

Xen Patches 'Worst'-Ever Virtual Machine Escape Vulnerability

Bug remained undetected for seven years and enabled complete control of host system.

One of the fundamental assumptions in virtualized computing environments is that code running in one virtual machine cannot escape its confines and directly access the host operating system and thereby other VMs running on the same physical server. Any vulnerability that enables a VM escape is considered a pretty big deal.

So news this week that a bug of precisely this nature had remained undetected for seven years in the popular Xen hypervisor is sure to prompt questions about the open source project’s security practices.

In an advisory issued yesterday, the Xen Project described the now patched vulnerability as one that could allow the administrator of a guest VM to escalate privileges and take complete control of the host system. The vulnerability gives attackers a way to bypass a mechanism in the Xen hypervisor that is designed to prevent guest VMs from making certain changes to table entries.

“The code to validate level 2 page table entries is bypassed when certain conditions are satisfied,” the Xen advisory noted. “This means that a  [guest VM] can create writeable mappings using super page mappings,” the alert said referring to a virtual memory management capability.

The issue is somewhat mitigated in situations where the host system, rather than a guest administrator, controls the guest VM, the alert noted. However, even here, it is possible for an untrusted guest administrator to trigger the flaw unless other measures are taken to prevent the guest VM from loading code into the kernel, the Xen security advisory warned.

Versions of Xen 3.4 and higher running on Intel x86 hardware are vulnerable to the flaw. Virtual machines hosted on ARM hardware are not susceptible to the threat. In addition, only guest VMs can exploit the vulnerability, Xen said.

The Xen alert attributed the discovery of the flaw to a researcher from Alibaba but provided no details on when the problem was first reported. The issue can be resolved by applying the patch publicly released this week, Xen said.

A researcher at the Qubes OS Project described the flaw as one the “worst” ever affecting Xen.  Qubes relies on Xen’s virtualization technology to implement what it describes as a security by isolation approach to OS security. Basically, the Qubes operating system is designed to let users compartmentalize their various activities, like Web browsing and banking, into separate VMs on the same machine so as to contain and limit the fallout from an attack.

“It is really shocking that such a bug has been lurking in the core of the hypervisor for so many years,” Marek Marczykowski, senior system developer at Invisible Things Lab, the developer of Qubes OS, said in a security bulletin. “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 plague the hypervisor ever again.”

Without such mechanisms, the Xen hypervisor makes little sense to organizations that would like to use it for security sensitive tasks, Marczykowski wrote. Given the critical nature of the Xen bug, Qubes developers have uploaded the patches directly to the current code repository instead of putting them through the usual one-week patch testing process, he said.

It's not the first time that the Xen hypervisor has been the focus of unfavorable attention over security flaws. Last October, for instance, Xen disclosed a bug that affected Amazon, Rackspace, and other cloud service providers. Earlier this year, the open source project disclosed another bug in a CD-ROM driver emulation feature that also enabled a VM escape.

The number of bugs being found in Xen is worrisome, according to Marczykowski. “For a type-1 hypervisor of the age and maturity of Xen, this simply should not be happening. If it does, it suggests the development process is not prioritizing security.”

 

Jai Vijayan is a seasoned technology reporter with over 20 years of experience in IT trade journalism. He was most recently a Senior Editor at Computerworld, where he covered information security and data privacy issues for the publication. Over the course of his 20-year ... View Full Bio
 

Recommended Reading:

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
Kelly Jackson Higgins
50%
50%
Kelly Jackson Higgins,
User Rank: Strategist
12/1/2015 | 8:27:30 AM
Re: 404 error on link
@JeffM787, thanks for the catch! I just fixed that broken URL. 
JeffM787
50%
50%
JeffM787,
User Rank: Strategist
11/30/2015 | 10:26:39 AM
404 error on link
The link referenced by "Marek Marczykowski, senior system developer at Invisible Things Lab, the developer of Qubes OS, said in a security bulletin." throws a link not found (404) error.
COVID-19: Latest Security News & Commentary
Dark Reading Staff 8/10/2020
Pen Testers Who Got Arrested Doing Their Jobs Tell All
Kelly Jackson Higgins, Executive Editor at Dark Reading,  8/5/2020
Researcher Finds New Office Macro Attacks for MacOS
Curtis Franklin Jr., Senior Editor at Dark Reading,  8/7/2020
Register for Dark Reading Newsletters
White Papers
Video
Cartoon Contest
Current Issue
Special Report: Computing's New Normal, a Dark Reading Perspective
This special report examines how IT security organizations have adapted to the "new normal" of computing and what the long-term effects will be. Read it and get a unique set of perspectives on issues ranging from new threats & vulnerabilities as a result of remote working to how enterprise security strategy will be affected long term.
Flash Poll
The Changing Face of Threat Intelligence
The Changing Face of Threat Intelligence
This special report takes a look at how enterprises are using threat intelligence, as well as emerging best practices for integrating threat intel into security operations and incident response. Download it today!
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2020-11976
PUBLISHED: 2020-08-11
By crafting a special URL it is possible to make Wicket deliver unprocessed HTML templates. This would allow an attacker to see possibly sensitive information inside a HTML template that is usually removed during rendering. Affected are Apache Wicket versions 7.16.0, 8.8.0 and 9.0.0-M5
CVE-2020-13179
PUBLISHED: 2020-08-11
Broker Protocol messages in Teradici PCoIP Standard Agent for Windows and Graphics Agent for Windows prior to 20.04.1 are not cleaned up in server memory, which may allow an attacker to read confidential information from a memory dump via forcing a crashing during the single sign-on procedure.
CVE-2020-8918
PUBLISHED: 2020-08-11
An improperly initialized 'migrationAuth' value in Google's go-tpm TPM1.2 library versions prior to 0.3.0 can lead an eavesdropping attacker to discover the auth value for a key created with CreateWrapKey. An attacker listening in on the channel can collect both 'encUsageAuth' and 'encMigrationAuth'...
CVE-2020-9244
PUBLISHED: 2020-08-11
HUAWEI Mate 20 versions Versions earlier than 10.1.0.160(C00E160R3P8);HUAWEI Mate 20 Pro versions Versions earlier than 10.1.0.270(C431E7R1P5),Versions earlier than 10.1.0.270(C635E3R1P5),Versions earlier than 10.1.0.273(C636E7R2P4);HUAWEI Mate 20 X versions Versions earlier than 10.1.0.160(C00E160R...
CVE-2020-9403
PUBLISHED: 2020-08-11
In PACTware before 4.1 SP6 and 5.x before 5.0.5.31, passwords are stored in a recoverable format, and may be retrieved by any user with access to the PACTware workstation.