Facilities are provided to secure guest runtime environments (GREs). Security policy specifications may be associated with GREs. A GRE's security policy may be specific to the GRE and may also include security policy inherited from higher levels such as a host operating environment. The security policy of a GRE specifies restrictions and/or permissions for activities that may be performed within the scope of execution of the GRE. A GRE's security policy may limit what the GRE's guest software may do within the GRE. Restrictions/permissions may be applied to objects such as files, configuration data, and the like. Security specifications may be applied to execution initiated within a GRE. A GRE's security specification may restrict/permit executable objects from loading and executing within the GRE. The executability or accessibility of objects may be conditioned on factors such as the health/integrity of the GRE, the host system, requested files, and others.