linux is vulnerable to arbitrary code execution. The vulnerabilitye exists as the kernel PV block backend expects the kernel thread handler to reset ring->xenblkd to NULL when stopped. However, the handler may not have time to run if the frontend quickly toggles between the states connect and disconnect. As a consequence, the block backend may re-use a pointer after it was freed. A misbehaving guest can trigger a dom0 crash by continuously connecting / disconnecting a block frontend.
git.launchpad.net/ubuntu-cve-tracker/tree/active/CVE-2020-29569
lists.debian.org/debian-lts-announce/2021/02/msg00018.html
lists.debian.org/debian-lts-announce/2021/03/msg00010.html
security.gentoo.org/glsa/202107-30
security.netapp.com/advisory/ntap-20210205-0001/
www.debian.org/security/2021/dsa-4843
xenbits.xenproject.org/xsa/advisory-350.html