The Xen Project has published Xen Security Advisories 252, 255, and 256 (XSA-252, XSA-255, and XSA-256, respectively). These XSAs do not affect the security of Qubes OS, and no user action is necessary.

These XSAs have been added to the XSA Tracker:

https://www.qubes-os.org/security/xsa/#252

https://www.qubes-os.org/security/xsa/#255

https://www.qubes-os.org/security/xsa/#256