Abstract: Various technologies and techniques are disclosed for increasing security in execution environments. A system is described for handling DLL calls made from untrusted code. An execution environment instantiates a lower trust process when a high trust process determines a need to call untrusted code. When the untrusted code calls a method in an original DLL, the execution environment loads a shim DLL into the lower trust process. The shim DLL has a clone of the method from the original DLL. A method for increasing security when processing calls from untrusted code is described. A shim DLL is created from an original DLL, and is deployed so an execution environment will load the shim DLL instead of the original DLL. When an execution environment receives a call from a caller DLL to the original DLL, the call is routed through the shim DLL. A pluggable validation system is also described.