A race condition vulnerability was found in the way the spice-vdagentd daemon handled new client connections. This flaw may allow an unprivileged local guest user to become the active agent for spice-vdagentd, possibly resulting in a denial of service or information leakage from the host. The highest threat from this vulnerability is to data confidentiality as well as system availability. This flaw affects spice-vdagent versions 0.20 and prior.
https://www.openwall.com/lists/oss-security/2020/11/04/1
https://lists.debian.org/debian-lts-announce/2021/01/msg00012.html