Heap-Based Buffer Overflow in spice-server GLZ Encoder

A critical integer truncation vulnerability (CVE-2026-105959) exists in the spice-server, specifically within the GLZ encoder dictionary restore path. The flaw occurs when a size_t allocation size is incorrectly truncated to an int when calling the memory allocation callback. An authenticated attacker acting as a SPICE client can leverage this vulnerability during the live migration of a virtual machine. By submitting a crafted max_encoders value in the migration data, the attacker forces the application to allocate an insufficient amount of memory, resulting in a heap buffer overflow. If successful, this attack could lead to arbitrary code execution within the context of the SPICE server process or induce a denial of service by crashing the virtual machine environment.

Impact

The vulnerability affects instances using spice-server, common in virtualization environments that provide remote display access to virtual machines. Successful exploitation allows an authenticated client to compromise the underlying virtualization host or service process. This presents a high risk for cloud providers, data centers, and enterprise environments managing virtualized infrastructure, potentially leading to cross-VM data access or service disruption.

Recommendation

• Monitor virtual machine migration logs for abnormal SPICE protocol traffic.
• Patch the spice-server component to the latest available vendor release addressing CVE-2026-105959.
• Review access controls for SPICE protocol endpoints to ensure only authorized clients can initiate or interact with VM migration sessions.