oxenstored maintains two datastructures about watches: one global trie, and one hashtable tracked per domain. When a xenbus reconnect is requested, watches are not cleared out of the global trie, so watches accumulate without bound in the global and per-domain structures, allowing a guest to exhaust host resources and cause a denial of service. Only systems using the OCaml Xenstored implementation are affected; the C Xenstored implementation is not. This is XSA-512.