VSHN’s Response to Zenbleed CVE-2023-20593

25. Jul 2023

Yesterday evening, on Monday, July 24th, 2023, at around 21:15 CEST / 12:15 PDT, our security team received a notification about a critical security vulnerability called „Zenbleed“ potentially affecting the cloud providers where VSHN’s customers systems run on.

This blog post provides details about Zenbleed and the steps taken to mitigate its risks.

What is Zenbleed?

Zenbleed, also known as CVE-2023-20593, is a speculative execution bug discovered by Google, related to but somewhat different from side channel bugs like Meltdown or Spectre. It is a vulnerability affecting AMD processors based on the Zen2 microarchitecture, ranging from AMD’s EPYC datacenter processors to the Ryzen 3000 CPUs used in desktop & laptop computers. This flaw can be exploited to steal sensitive data stored in the CPU, including encryption keys and login credentials.

VSHN’s Response

VSHN immediately set up a task force to discuss this issue, including the team of one of our main cloud providers ( in a call to determine choices of action; among possible options, were contemplated ideas like isolating VSHN customers on dedicated nodes, or patching the affected systems directly.

At around 22:00 CEST, the cloud provider decided after a fruitful discussion with the task force that the best approach was to implement a microcode update. Since Zenbleed is caused by a bug in CPU hardware, the only possible direct fix (apart from the replacement of the CPU) consists of updating the CPU microcode. Such updates can be applied by updating the BIOS on affected systems, or applying an operating system kernel update, like the recently released new Linux kernel version that addresses this vulnerability.

Zenbleed isn’t limited to just one cloud provider, and may affect customers operating their own infrastructure as well. We acknowledged that addressing this vulnerability is primarily a responsibility of the cloud providers, as VSHN doesn’t own any infrastructure that could directly be affected.

The VSHN task force handed the monitoring over to VSHN Canada to test the update as it rolled out to production systems, who stayed in close contact to ensure there were no QoS degradations after the microcode update.

Aftermath successfully finished its work at 01:34 CEST / 16:34 PDT. All VSHN systems running on that provider have been patched accordingly, and the tests carried show that this specific vulnerability has been fixed as required. VSHN Canada confirmed that all systems were running without any problems.

We will continue to monitor this situation and to inform our customers accordingly. All impacted customers will be contacted by VSHN. Please do not hesitate to contact us for more information.

Adrian Kosmaczewski

Adrian Kosmaczewski ist bei VSHN für den Bereich Developer Relations zuständig. Er ist seit 1996 Software-Entwickler, Trainer und veröffentlichter Autor. Adrian hat einen Master in Informationstechnologie von der Universität Liverpool.

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