A flaw was found in spice-server. The GLZ encoder dictionary restore path truncates a size_t allocation size to int when calling the malloc callback, allowing a malicious authenticated SPICE client during VM live migration to trigger a massive heap buffer overflow by sending a crafted max_encoders value in migration data.
This vulnerability is only exploitable during VM live migration by an authenticated SPICE client. If live migration is not required, disabling it eliminates the attack surface. If live migration is needed, restrict SPICE client connections to trusted networks using firewall rules and enforce strong authentication (TLS with mutual certificate validation, or SASL with strong credentials) to limit who can connect as a SPICE client.