DEF CON 23 - Hijacking Arbitrary .NET Application Control Flow

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Hijacking Arbitrary .NET Application Control Flow Topher Timzen

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Security Researcher, Intel Security Trainer TopherTimzen.com @TTimzen #whoami

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Overview .NET? Runtime Attacks Modify Control Flow Machine Code Editing Managed Heap

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Tools Released Use .NET to attack Using Objects on the Heap Why are we Here?

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CLR Attacks Controlling the Common Language Runtime Accessing raw objects on Managed Heap Manipulate AppDomains • Controlling all Loaded Code • Controlling Just-In-Time Compilation

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Attack With ASM Manipulate Resources Attack methods at ASM level Alter application control flow

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Runtime .NET Process CLR (2.0/4.0) & AppDomains Assemblies (.EXE and .DLL(s)) Objects Properties Fields Instance Methods Classes Methods Logic

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Gray Frost & Gray Storm The Tools

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Gray Frost

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Gray Frost Payload delivery system C++ .NET CLR Bootstrapper Creates or injects 4.0 runtime Capability to pivot into 2.0 runtime Contains raw payload 2 Rounds GrayFrostCpp GrayFrostCSharp • C# Payload

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Round 1 .NET Process

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Round 1 Mscoree GrayFrostCpp

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Round 1 GrayFrostCpp

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Round 1 GrayFrostCSharp GrayFrostCpp

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Round 2 .NET Process

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Round 2 .NET Process GrayFrostCSharp

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Round 2 .NET Process payload void main() GrayFrostCSharp

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Round 2 .NET Process Payload

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.NET Process Pivoting Between runtimes

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Mscoree GrayFrostCpp Pivoting Between runtimes

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GrayFrostCpp Pivoting Between runtimes

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GrayFrostCSharp GrayFrostCpp Pivoting Between runtimes

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GrayFrostCSharp GrayFrostCpp Pivoting Between runtimes

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GrayFrostCpp Pivoting Between runtimes

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GrayFrostCSharp GrayFrostCpp Pivoting Between runtimes

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GrayFrostCSharp GrayFrostCpp Pivoting Between runtimes

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Gray Storm

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Gray Storm Reconnaissance and In-memory attack payload Features Attacking the .NET JIT Attacking .NET at the ASM level ASM and Metasploit payloads Utilize objects on the Managed Heap

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Gray Storm Usage

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Controlling the JIT Method Tables contain address of JIT stub for a class’s methods. During JIT the Method Table is referenced We can control the address Lives after Garbage Collection

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Controlling the JIT

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Controlling the JIT

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Control Flow Attacks .NET uses far and relative calls 0xE8; Call [imm]  0xFF 0x15; Call dword segmentRegister[imm] relCall = dstAddress - (currentLocation+ lenOfCall)

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ASM Payloads Address of a method known through Reflection Overwrite method logic with new ASM Steal stack parameters Change events

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ASM Payloads Change return TRUE to return FALSE Password validation Key & Licensing validation SQL Sanitization Destroy security Mechanisms Overwrite logic Update Mechanisms

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ASM Payloads

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ASM Payloads Metasploit Hand Rolled Portable Environment Block (PEB) changes

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Portable Environment Block http://www.tophertimzen.com/blog/shellcodeDotNetPEB/

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Object Hunting in Memory

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Managed Heap Storage point for .NET Objects New reference objects added to heap Garbage Collector removes dead objects

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Managed Heap Storage point for .NET Objects New reference objects added to heap Garbage Collector removes dead objects Let’s manipulate it!

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Object Hunting in Memory Objects are IntPtrs Point to Object Instance on Managed Heap All instantiated objects of the same class share the same Method Table Reflection Object Hunting Win

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Finding Objects at Runtime i. Construct an object and find location of Managed Heap ii. Signature instantiated type iii. Scan Managed Heap for object pointers iv. Convert object pointers to raw objects v. ???? vi. PROFIT

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Construct an Object Use Reflection to invoke a constructor Can instantiate any object If a constructor takes other objects, nullify them https://gist.github.com/tophertimzen/010b19fdbde77f251414

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IntPtr = 024e9fe8 024e9fe8 (Object) 00000005 00000001 00000000 IntPtr = 5 STACK 024e9fe8 (Object) L H https://gist.github.com/tophertimzen/812aa20dbe23cb42756d Find location of Managed Heap

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IntPtr = 024e9fe8 024e9fe8 (Object) 00000005 00000001 00000000 IntPtr = 5 STACK Managed Heap 024e9fe8 (Object) L H https://gist.github.com/tophertimzen/812aa20dbe23cb42756d Find location of Managed Heap

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IntPtr = 024e9fe8 024e9fe8 (Object) 00000005 00000001 00000000 IntPtr = 5 STACK 024e9fe8 (Object) L H https://gist.github.com/tophertimzen/812aa20dbe23cb42756d Find location of Managed Heap

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IntPtr = 024e9fe8 024e9fe8 (Object) 00000005 00000001 00000000 STACK L H https://gist.github.com/tophertimzen/812aa20dbe23cb42756d Find location of Managed Heap

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Signature instantiated type Object Instances contain a Method Table pointer to their corresponding type. (x86) Bytes 0-3 are the Method Table (MT) Bytes 4-7 in MT is Instance Size 0:009> dd 024e9fe8 024e9fe8 00774828 0000038c 00000001 00000000

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Signature instantiated type Object Instances contain a Method Table pointer to their corresponding type. (x64) Bytes 0-7 are the Method Table (MT) Bytes 8-11 in MT is Instance Size 0:008> dd 00000000024e9fe8 00000000`0286b8e0 ea774828 000007fe

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Scan Managed Heap Scan down incrementing by size of object Scan linearly up to top of heap Compare object’s Method Table to the reference If they match, get IntPtr address of object

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Convert object ptr -> raw obj STACK Refer (System.IntPtr) pointer(024ea00c ) pointer(024ea00c ) L H https://gist.github.com/tophertimzen/1da2b0aab6245ed1c27b

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Convert object ptr -> raw obj STACK Refer (System.IntPtr) pointer(024ea00c ) pointer(024ea00c ) L H https://gist.github.com/tophertimzen/1da2b0aab6245ed1c27b

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Convert object ptr -> raw obj Refer (GrayStorm.testClass) pointer(024ea00c ) STACK L H https://gist.github.com/tophertimzen/1da2b0aab6245ed1c27b

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????

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PROFIT

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Superpowers and Things? Change Keys Change Fields / Properties Call Methods With arguments!

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Automation

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Automation GrayFrost can be used with automated payloads

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Constructing Attack Chains

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How to construct attack chains Gray Wolf / IL Decompiler  Find Methods, Fields & Properties of interest  Locate meaningful objects  Discover high level control flow Gray Storm “Debugging” functionality  Breakpoint at constructors or methods from Method Pointers  Use with WinDbg Utilize DLL Hijacking!

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Hybrid .NET/ASM Attacks Hybrid C#/ASM code in .NET Encrypting .NET payloads and unwinding Encrypting ASM Payloads

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Payload System C# is easy Can use Gray Frost in any application Low and High level gap is easy

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.NET Hacking Space Small Few tools Mostly hacking WoW Lots of PowerShell Previous DEF CON talks DEF CON 18 & 19 - Jon McCoy

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Conclusion Arbitrary .NET applications can be injected and changed New .NET attack possibilities New tools that support automation Get Gray Frost and Storm github.com/graykernel

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Questions? Contact Me @TTimzen https://www.tophertimzen.com Get Gray Frost and Storm github.com/graykernel White Papers Hijacking Arbitrary .NET Application Control Flow Acquiring .NET Objects from the Managed Heap