The Xen Project has published Xen Security Advisories 258 and 259 (XSA-258 and XSA-259, 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/#258
https://www.qubes-os.org/security/xsa/#259