The Xen Project reports:
A domain's xenoprofile state contains an array of per-vcpu information... This array is leaked on domain teardown. This memory leak could -- over time -- exhaust the host's memory. The following parties can mount a denial of service attack affecting the whole system:
A malicious guest administrator via XENOPROF_get_buffer. A domain given suitable privilege over another domain via XENOPROF_set_passive (this would usually be a domain being used to profile another domain, eg with the xenoprof tool).
The ability to also restart or create suitable domains is also required to fully exploit the issue. Without this the leak is limited to a small multiple of the maximum number of vcpus for the domain.