CVE-2026-105959

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 rated as Important rather than Critical because successful exploitation requires valid client authentication and must coincide with an active virtual machine live migration window. In Red Hat virtualization environments, SPICE services are typically hosted by QEMU processes confined by sVirt SELinux protections, which restricts host system compromise even if process crash or code execution occurs. Environments that configure headless guests, use alternative display protocols such as VNC, or isolate management access are not susceptible to untrusted client connections.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

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.

--- CME Mitigation Guidance (2026-10-20) --- Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.

The highest-value action is to prevent integer truncation of size_t allocation calculations to int when invoking the GlzEncoderUsrContext::malloc callback in the GLZ dictionary restore path: upgrade to the fixed Spice/Spice Server builds, which prevent truncation of size_t allocation sizes to int when invoking the GLZ dictionary malloc callback, closing all 2 injection vectors (crafted SPICE_MSGC_MIGRATE_DATA message, malicious max_encoders field in GlzEncDictRestoreData). Until patched, this is a concern on 64-bit Linux hosts running SPICE server, so Disable VM live migration if not required, restrict SPICE client access to trusted networks using firewall rules, and enforce strong authentication via SASL or TLS with mutual certificate validation. As a compensating measure, Run SELinux in enforcing mode to confine the SPICE server process domain and restrict unauthorized system access if the heap overflow is exploited. These controls limit blast radius and contain exploitation, but they do not fix the underlying integer truncation defect — apply the upstream patch to fully remediate.

Highest-impact CME: CME-301 SELinux (Enforcing Mode) (medium)