KB5009557: Windows Server 2019 Security Update (January 2022)

An attacker with any code execution inside one Hyper-V guest can interact with processes inside other guests on the same physical Hyper-V host, bypassing the isolation that is supposed to keep tenants separate. The exact scope of the cross-guest interaction depends on what Hyper-V capabilities are reachable, but the security guarantee being violated is fundamental.

Hyper-V is the Windows hypervisor that isolates guest VMs from each other and from the host. A flaw in Hyper-V's privilege boundary lets an attacker who already has code execution inside one guest VM interact with processes hosted in another guest on the same physical host. This is not a full guest-to-host escape — it is a guest-to-guest isolation breach.

Probably yes if any of these apply:

A multi-tenant Hyper-V host runs different customers' workloads side by side. One customer is compromised through their own application stack; the attacker uses the Hyper-V EoP to reach into another customer's VM on the same physical host, read process memory, and steal credentials. The shared-host trust model is broken.