Xen Orchestra before 6.9.0 contains an improper access control vulnerability that allows any authenticated user to become global administrator by abusing the unprotected vm.importFromEsxi and vm.importMultipleFromEsxi methods. Attackers can point xo-server at a malicious ESXi host serving a crafted .vmx file with __proto__.permission set, polluting Object.prototype so permission-less accounts inherit admin rights and enabling remote code execution.