spice-server EUVD-2026-102846

Exploitation requires (1) an authenticated SPICE client connection to the target VM (PR:L), and (2) a VM live migration to be in progress, because the vulnerable code is the GLZ encoder dictionary restore path that only runs when processing migration data. The specific trigger is a crafted oversized max_encoders value whose size_t allocation size is truncated to int in the malloc callback. Limiting factors: the attacker must already be an authenticated SPICE client, the live-migration window must be reachable (contributing to AC:H), and GLZ (LZ) compression/encoding must be in use for the session. This is not exploitable against a default, idle, non-migrating VM, which meaningfully narrows real-world opportunity despite the network attack vector.

This is a genuine but conditional risk, not a drop-everything emergency. The provided CVSS 3.1 vector (AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H, base 7.5) tells a consistent story: network-reachable (SPICE client), but high attack complexity (AC:H) and low-privilege-but-authenticated (PR:L), with full CIA impact from a heap overflow. The AC:H is corroborated by the description, which requires a specific race/state window - the vulnerability lives in the GLZ encoder dictionary restore path that only executes during VM live migration - so an attacker cannot trigger it on demand against a static, non-migrating VM. No EPSS score, no CISA KEV listing, and no public POC are present in the input, so exploitation signals point to no confirmed or widespread exploitation at this time. The description's 'malicious authenticated SPICE client' aligns correctly with PR:L, so there is no network-vs-local conflict to flag. Net assessment: a legitimately high-severity memory-corruption bug in a virtualization component with plausible RCE/host-impact, but gated behind authentication AND the live-migration window, making opportunistic mass exploitation unlikely. Prioritize patching on multi-tenant or untrusted-guest virtualization hosts; it is lower urgency for single-tenant deployments that rarely migrate or tightly control SPICE access.

An authenticated but malicious SPICE client connected to a VM waits for (or induces) a live migration, then supplies a crafted oversized max_encoders value in the GLZ dictionary migration data. The size_t-to-int truncation produces an undersized malloc while the code writes against the original large size, causing a massive heap buffer overflow on the receiving spice-server that can crash the host service or potentially lead to code execution. No public exploit code is identified at time of analysis, and the high attack complexity (dependence on the migration window) limits reliability.