The Xen Project has published Xen Security Advisories 296, 298, 301, and 303 (XSA-296, XSA-298, XSA-301, and XSA-303, 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/#296

https://www.qubes-os.org/security/xsa/#298

https://www.qubes-os.org/security/xsa/#301

https://www.qubes-os.org/security/xsa/#303