A flaw was found in the way spice-client processed certain messages sent from the server. An attacker, having control of malicious spice-server, could use this flaw to crash the client or execute arbitrary code with permissions of the user running the client. spice-gtk versions through 0.34 are believed to be vulnerable.
https://usn.ubuntu.com/3659-1/
https://security.gentoo.org/glsa/201811-20