RETBleed security patch

Security Jul 15, 2022

You probably heard of it: there's a new CPU vulnerability in town, affecting various CPUs, both Intel and AMD (and likely even non-x86 architectures: it's a pretty "wide" problem). So here is the software mitigation for it, directly added inside Xen hypervisor.

To update, follow this guide. You can also join the discussion on our community forum. Hosts reboot necessary after this update.


RETbleed is a speculative execution attack on x86-64 processors, including some recent Intel and AMD chips. You can read the original announcement from Computer Security Group at this address:

Despite sounding similar to previous speculative execution attacks targeting indirect jumps (the whole Spectre family), RETbleed exploits return instructions. And it's a big deal, since it defeats the existing Spectre-like mitigations in place. Not convinced? See this demo:

In terms of affected hardware, here is a list of tested CPUs against it:


Due to this hardware security flaw, an attacker might be able to infer the contents of arbitrary host memory, including memory assigned to other guests.



Olivier Lambert

Along with Gaël Duperrey

Vates CEO & co-founder, Xen Orchestra and XCP-ng project creator. Enthusiast entrepreneur and Open Source advocate. A very happy Finnish Lapphund owner.