Various technologies and techniques are disclosed that use code access security for providing runtime accessibility checks. A request is received from a first program to access at least one private member of a second program at runtime. If the first program has a greater than or equal security context than the second program, then the first program is granted access to the at least one private member of the second program. This code access security check can be provided in a framework environment that is responsible for managing programs that are from unknown or untrusted sources.