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Maxstack2 localsinitclasssecretsecretv0classhackv1

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Unformatted text preview: ture 16 13 .field public int32 'data' .method static void Main() cil managed { .entrypoint .maxstack 2 .locals init (class [Secret]Secret V_0, class Hack V_1) newobj instance void [Secret]Secret::.ctor() stloc.0 newobj instance void Hack::.ctor() stloc.1 ldloc.0 type confusion… stloc.1 ldloc.1 ldfld int32 Hack::'data' call void [mscorlib]System.Console::WriteLine(int32) ret } …but this code might execute, nevertheless! SY32 Secure Computing, Lecture 16 14 Explanation • Assembly that fails verification may run if loaded Assembly from local disk, because such code is trusted fully by default fully • Same assembly downloaded from a web server Same will normally not be executed will • Exact behaviour depends on how code access Exact security policy has been configured security SY32 Secure Computing, Lecture 16 15 Problems • • IL verification is hard to implement correctly Example: bugs in Java's bytecode verifier March 1996 March & May 1997 April 1999 March 2002 January 2003 SY32 Secure Computing, Lecture 16 16 Restricted Environments • • • The Java sandbox .NET application domains .NET isolated storage SY32 Secure Computing, Lecture 16 17 The Classic Java Sandbox • Applets from the Internet are not trusted and must execute in a sandbox sandbox Cannot run programs on client machine No access to local file system Network access restricted to originating site • Applications from local disk are implicitly trusted Applications and have full privileges of executing user and • Restri...
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