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Object Oriented Code RE with HexraysCodeXplorer

The document discusses challenges in reversing object-oriented C++ code and malware. It presents approaches used by the HexRaysCodeXplorer plugin for IDA to assist with reconstructing object types and navigating virtual methods in decompiled code. The plugin allows partially reconstructing object types from initialization routines and traversing related virtual methods. It has features for position independent code and supports IDA x64.

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Object Oriented Code RE with HexRaysCodeXplorer Eugene Rodionov @vxradius Alex Matrosov @matrosov
Agenda * Object Oriented Code Reversing Challenges -- virtual methods -- templates * Reversing Object Oriented Malware -- Flamer -- Sednit * HexRaysCodeXplorer in use
Modern C++ Malware for Targeted Attacks
Why reversing C++ code is a hard problem? Virtual Methods & Templates
Virtual Methods class Cat { private: int _weight; public: Cat(int weight) : _weight(weight) {}; int eat(int food) { return _weight += food; }; }; int _tmain(int argc, _TCHAR* argv[]) { Cat* cat = new Cat(130); int newWeigth = cat->eat(20); } class Animal { protected: int _weight; public: Animal(int weight) : _weight(weight) {}; virtual int eat(int food) = 0; }; class Cat : Animal { public: Cat(int weight) : Animal(weight) {}; virtual int eat(int food) { return _weight += food; }; }; int _tmain(int argc, _TCHAR* argv[]) { Animal* cat = new Cat(130); int newWeight = cat->eat(20); } vs
Virtual Methods class Cat { private: int _weight; public: Cat(int weight) : _weight(weight) {}; int eat(int food) { return _weight += food; }; }; int _tmain(int argc, _TCHAR* argv[]) { Cat* cat = new Cat(130); int newWeigth = cat->eat(20); } class Animal { protected: int _weight; public: Animal(int weight) : _weight(weight) {}; virtual int eat(int food) = 0; }; class Cat : Animal { public: Cat(int weight) : Animal(weight) {}; virtual int eat(int food) { return _weight += food; }; }; int _tmain(int argc, _TCHAR* argv[]) { Animal* cat = new Cat(130); int newWeight = cat->eat(20); } vs
Virtual Function Tables Class A vfPtr attr_1 attr_2 A::vfTable A::a1() A::a2() A::a3() RTTI Object Locator signature pTypeDescriptor pClassDescriptor meta
Virtual Function Tables Class A vfPtr attr_1 attr_2 A::vfTable A::a1() A::a2() A::a3() RTTI Object Locator signature pTypeDescriptor pClassDescriptor meta
Virtual Function Tables * lead to indirect method calls -- difficult to analyze statically * initialized in constructors -- need to track back object creation
C++ Templates * extra code to analyze -- another way to create polymorphic types * problematic to recognize standard library code (FLIRT) -- playing with compiler optimization options std::vector<int> std::vector<char> std::vector<std::string> std::vector<custom_type>
C++ Code Reconstruction Problems * Object identification -- type reconstruction * Class layout reconstruction -- Identify constructors/destructors -- Identify class members -- Local/global type reconstruction -- Associate object with exact method calls * RTTI reconstruction -- vftable reconstruction -- Associate vftable object with exact object -- class hierarchy reconstruction
Reversing Object Oriented Malware Practical Approaches: REconstructing Flamer Framework
REconstructing Flamer Framework Vector<Command Executor> DB_Query ClanCmd Vector<Task> IDLER CmdExec Vector<DelayedTasks> Euphoria Share Supplier Vector<Consumer> Mobile Consumer Cmd Consumer MunchSniffer FileFinder FileCollect Driller GetConfig LSS Sender Frog Beetlejuice Lua Consumer Media Consumer http://www.welivesecurity.com/2012/08/02/flamer-analysis-framework-reconstruction/
REconstructing Flamer Framework Vector<Command Executor> DB_Query ClanCmd Vector<Task> IDLER CmdExec Vector<DelayedTasks> Euphoria Share Supplier Vector<Consumer> Mobile Consumer Cmd Consumer MunchSniffer FileFinder FileCollect Driller GetConfig LSS Sender Frog Beetlejuice Lua Consumer Media Consumer http://www.welivesecurity.com/2012/08/02/flamer-analysis-framework-reconstruction/
Identifying Used Types * Smart pointers * Strings * Vectors to maintain objects * Custom data types: -- tasks -- triggers -- and etc.
Data Types Being Used: Smart pointers struct SMART_PTR { void *pObject; // pointer to the object int *RefNo; // reference counter };
Data Types Being Used: Smart pointers
Data Types Being Used: Vectors struct VECTOR { void *vTable; // pointer to the virtual table int NumberOfItems; // self-explanatory int MaxSize; // self-explanatory void *vector; // pointer to buffer with elements }; * Used for handling objects: -- tasks -- triggers
Data Types Being Used: Strings struct USTRING_STRUCT { void *vTable; // pointer to the table int RefNo; // reference counter int Initialized; wchar_t *UnicodeBuffer; // pointer to unicode string char *AsciiBuffer; // pointer to ASCII string int AsciiLength; // length of the ASCII string int Reserved; int Length; // Length of unicode string int LengthMax; // Size of UnicodeBuffer };
Approaching Flamer * Identify Object Constructors * Reconstruct Object Attributes * Reconstruct Object Methods Type reconstruction Control Flow Graph Reconstruction
Identifying Object Constructors
REconstructing Object’s Attributes
REconstructing Object’s Attributes
REconstructing Object’s Methods
REconstructing Object’s Methods
REconstructing Object’s Methods
Reversing Object Oriented Malware Practical Approaches: REconstructing XAgent Framework
XAgent Framework Communication Channels Vector<IAgentChannel> AgentKernel Local Storage Cryptor Agent Modules Vector<IAgentModule> AgentKernel Module FileSystem Channel Controller DNameNode Module Remote KeyLogger Process Retranslator Module WinHttp http://www.welivesecurity.com/2014/10/08/sednit-espionage-group-now-using-custom-exploit-kit/
Object Interconnection: IAgentModule struct IAgentModule { LPVOID receiveMessage; LPVOID sendMessage; LPVOID getModuleId; LPVOID setModuleId; LPVOID executeModule; }; AgentKernel Module FileSystem Module Remote Keylogger Process Retranslator Module IAgentModule
Exploring RTTI* * recover type names * reconstruct class hierarchy * identify object virtual function tables * IDA ClassInformer plugin
Exploring RTTI* * recover type names * reconstruct class hierarchy * identify object virtual function tables * IDA ClassInformer plugin
XAgent: LocalDataStorage Local DataStorage Registry reader/writer File reader/writer
XAgent: Cryptor
XAgent: Cryptor encrypted message salt (4 bytes) RC4key plain text
XAgent: IReservedApi
XAgent: Identifying Used Types * Strings: std::string * Containers to maintain objects: -- std::vector -- std::list
XAgent: Identifying Used Types * Strings: std::string * Containers to maintain objects: -- std::vector -- std::list
HexRaysCodeXplorer
HexRaysCodeXplorer since 2013 * CodeXplorer V1.0 released on REcon’2013 * First third-party plugin for Hex-Rays Decompiler * v1.0 supports IDA v6.4 and Decompiler for x86 v1.8
HexRaysCodeXplorer Features * Hex-Rays decompiler plugin x86/x64 * The plugin was designed to facilitate static analysis of: -- object oriented code -- position independent code * The plugin allows to: -- partially reconstruct object type -- navigate through decompiled virtual methods
Hex-Rays Decompiler Plugin SDK * At the heart of the decompiler lies ctree structure: -- syntax tree structure -- consists of citem_t objects -- there are 9 maturity levels of the ctree structure
* Type citem_t is a base class for: -- cexpr_t – expression type -- cinsn_t – statement type * Expressions have attached type information * Statements include: -- block, if, for, while, do, switch, return, goto, asm * Hex-Rays provides iterators for traversing the citem_t objects within ctree structure: -- ctree_visitor_t, ctree_parentee_t Hex-Rays Decompiler Plugin SDK citem_t cexpr_t cinsn_t
* Type citem_t is a base class for: -- cexpr_t – expression type -- cinsn_t – statement type * Expressions have attached type information * Statements include: -- block, if, for, while, do, switch, return, goto, asm * Hex-Rays provides iterators for traversing the citem_t objects within ctree structure: -- ctree_visitor_t, ctree_parentee_t Hex-Rays Decompiler Plugin SDK citem_t cexpr_t cinsn_t
DEMO time :)
HexRaysCodeXplorer: Gapz Position Independent Code
HexRaysCodeXplorer: Virtual Methods IDA’s ‘Local Types’ is used to represent object type
HexRaysCodeXplorer: Virtual Methods IDA’s ‘Local Types’ is used to represent object type
HexRaysCodeXplorer: Virtual Methods * Hex-Rays decompiler plugin is used to navigate through the virtual methods
HexRaysCodeXplorer: Object Type REconstruction * Hex-Rays’s ctree structure may be used to partially reconstruct object type * Input: -- pointer to the object instance -- object initialization routine entry point * Output: -- C structure-like object representation
HexRaysCodeXplorer: Object Type REconstruction * citem_t objects: -- memptr, idx, memref -- call, ptr, asg
HexRaysCodeXplorer: Object Type REconstruction * citem_t objects: -- memptr, idx, memref -- call, ptr, asg
HexRaysCodeXplorer: Object Type REconstruction // reference of DWORD at offset 12 in buffer a1 *(DWORD *)(a1 + 12) = 0xEFCDAB89;
HexRaysCodeXplorer: v1.7 [NSEC Edition] Automatic virtual table identification + Type reconstruction
HexRaysCodeXplorer: v1.7 [NSEC Edition] * Automatic virtual table identification
HexRaysCodeXplorer: v1.7 [NSEC Edition] * Automatic virtual table identification
HexRaysCodeXplorer: v1.7 [NSEC Edition] * Automatic virtual table identification * Support for IDA Pro x64 * Bugfixes
DEMO time :)
HexRaysCodeXplorer: Next plans * Switch to IdaPython
Why python?
HexRaysCodeXplorer: Next plans * Switch to IdaPython * Further research & development: -- find cross-references to object attributes -- handling nested structures -- code similarity based on data flow analysis
Thank you for your attention! http://REhints.com @Rehints https://github.com/REhints/HexRaysCodeXplorer