Tag Archives: Xen

Responding to the recent ZombieLand 2 TSX Vulnerabilities

These vulnerabilities can only be exploited by attackers who have already compromised a system. Practice standard security precautions and install updates from hardware vendors and for your software (links provided below) when they become available. Resolution for vendors that offer cloud computing will have a more involved decision making process to consider (see below).

Early last week, security researchers disclosed security researchers disclosed further vulnerabilities within Intel’s processors.

How severe are these vulnerabilities?
These vulnerabilities ca be classed as medium severity. An attacker must already have compromised your system in order to exploit these vulnerabilities. This most recent set of vulnerabilities collectively known as ZombieLoad 2 or Transactional Synchronization Extensions (TSX) Asynchronous Abort affect Intel processors produced in the last approx. 2.5 years (August 2017 onwards).

For full technical details of these vulnerabilities, please see this page from Intel and this page from the security researchers. In summary these vulnerabilities according to the researchers allow “a malicious program to exploit internal CPU buffers to get hold of secrets currently processed by other running programs” leading to “these secrets such as browser history, website content, user keys, and passwords, or system-level secrets, such as disk encryption keys” being used by other running programs.

Of particular note are the performance implications for protecting virtual machines. If your organisation is running potentially untrusted code within virtual machines, protecting that environment will incur a performance penalty. You may need to carry out a risk assessment to determine if enabling these performance reducing mitigations outweigh the risk of putting your virtual machines at risk. Nested virtual machines will be most affected by the performance penalty.

How can I protect my organisation and myself from these vulnerabilities?
These most recent vulnerabilities can be mitigated by updating the firmware (defined) of your system. This is sometimes referred to as the UEFI / BIOS (defined) of your system.

They will be made available separately by the manufacturer of your motherboard of your system for servers, desktops and laptops or the motherboard (defined) manufacturer for any custom-built systems you may have. You will have to determine from the updates those vendors issue if they are available for the products that you own.

In addition, operating system vendors and virtualisation software vendors have made patches available (links provided below).

Thank you.


HP Enterprise:

Fedora (referring to the Xen virtual machine (see also below):

Red Hat:













Performance impact to Xen:

Security advisory:

Further information:

VMware Performance Impact Statement addressing mitigations for Machine Check Exception on Page Size Change (MCEPSC) CVE-2018-12207:

Intel Lazy Floating Point Vulnerability: What you need to know

Update: 24th July 2018:
I have updated the list of vendor responses below to include further Red Hat versions and CentOS:

Red Hat Enterprise Linux 6:

Red Hat Enterprise Linux 5 and 7:

CentOS 6:

CentOS 7:


On Wednesday of last week, a further vulnerability affecting Intel CPUs (defined) was disclosed.

TL;DR: Keep your operating system up to date and you should be fine.

What makes this vulnerability noteworthy?
According to Intel’s security advisory; this is an information disclosure issue. Similar to Spectre/Meltdown the flaw is the result of a performance optimization (used when saving and restoring the current state of applications as a system switches from one application to another). A feature known as Lazy Floating Point (defined) Unit (FPU) is used to save and restore registers (defined) within the CPU used to store floating point numbers (non-integers numbers, namely decimal numbers).

The issue is that these registers may be accessed by another application on the same system. If the registers are storing for example results of performing cryptographic equations for a key you have just created or used to decrypt data, the attacker could use this data to infer what the actual key is. The same applies for any type of data the registers store; that data can be used to infer what the previous contents were via a speculative execution side channel.

This vulnerability has been rated as moderate since it is difficult to exploit via a web browser (in contrast to Spectre) and the updates will be a software update only; no microcode (defined) and/or firmware (defined) updates will be necessary. With exploitation via a web browser being difficult; this vulnerability will likely instead be exploited from the victim system (at attacker will need to have already compromised your system).

How can I protect myself from this vulnerability?
Please note; AMD CPUs are NOT affected by this vulnerability.

The following vendors have responded to this vulnerability with software updates now in progress. Separately Red Hat has completed their updates for Red Hat Linux 5, 6 and 7 (with further applicable updates still in progress).

Other vendors responses are listed below. Thank you:

Amazon Web Services

Apple (currently release notes for an update to macOS to resolve the vulnerability)


Intel’s Security Advisory


Microsoft Windows


Xen Project

Xen Project Patches 7 Year Old Critical Security Vulnerability

In late October the Xen Project who is the maintainer of its very popular Xen Project virtualization software (defined) released a series of security advisories to resolve 9 security issues (consisting of 8 CVEs (defined)) within their software. The most serious of which (described in this advisory) has been present within the software for the last 7 years (but went undetected during that time).

Why Should These Issues Be Considered Important?
The most serious issue which affects version 3.4 (onwards) of the Xen Project involved how a guest server (namely a server which only exists in software rather than a physical device enabling multiple servers to exist on a single physical server) accesses the memory of the physical server within which it resides. This was due to code that validates access to the page table (see page 10 and 11 of this PDF for a definition of a level 2 table specific to this vulnerability. This slide deck explains the more general concept) being bypassed under certain conditions meaning that the guest server (if under the control of an attacker or malware) could have escalated it’s privileges to completely control the physical server.

The remaining 8 security issues could also cause a severe impact to your server infrastructure since they are denial of service issues (defined).

How Can I Protect Myself From These Issues?
While mitigations are available for the majority of these issues, it is recommended to apply the necessary security updates if you use the Xen Project virtualization software within your organization.

The main Xen security advisories page is located here. Links to the appropriate advisories with steps to install the necessary updates are provided below:

Thank you.