Briefing for:

Hacking Windows Internals

Cesar CerrudoCesar Cerrudo

ArgenissArgeniss

www.appsecinc.com

Hacking Shared Sections

Shared Section definition Using Shared Sections Tools Problems Searching for holes Exploitation Microsoft vulnerabilities Other vendors vulnerabilities Solutions Conclusions References

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Shared Section

Basically a Shared Section is a portion of memory shared by a process, mostly used as an IPC (Inter Process Communication) mechanism. Shared Memory. File Mapping. Named or Unnamed.

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Using Shared Sections

Loading binary images by OS. Process creation. Dll loading.

Mapping kernel mode memory into user address space !?. Used to avoid kernel transitions.

Sharing data between processes. GDI and GUI data, pointers !?, counters, any data.

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Using Shared Sections

Creating a shared section

HANDLE CreateFileMapping( HANDLE hFile, // handle to file (file mapping) //or 0xFFFFFFFF (shared memory) LPSECURITY_ATTRIBUTES lpAttributes, // security DWORD flProtect, // protection DWORD dwMaximumSizeHigh, // high-order DWORD of size DWORD dwMaximumSizeLow, // low-order DWORD of size LPCTSTR lpName // object name (named)

//or NULL (unnamed));//returns a shared section handle

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Using Shared Sections

Opening an existing shared section

HANDLE OpenFileMapping(

DWORD dwDesiredAccess, // access mode (FILE_MAP_WRITE // FILE_MAP_READ, etc.)

BOOL bInheritHandle, // inherit flag

LPCTSTR lpName // shared section name

);//returns a shared section handle

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Using Shared Sections

Mapping a shared section

LPVOID MapViewOfFile( HANDLE hFileMappingObject, // handle to created/opened

// shared section DWORD dwDesiredAccess, // access mode(FILE_MAP_WRITE

// FILE_MAP_READ, etc.) DWORD dwFileOffsetHigh, // high-order DWORD of offset DWORD dwFileOffsetLow, // low-order DWORD of offset SIZE_T dwNumberOfBytesToMap // number of bytes to map); //returns a pointer to begining of shared section memory

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Using Shared Sections

Ntdll.dll Native API NtCreateSection() Creates a new section NtOpenSection() Opens an existing section NtMapViewOfSection() Map a section on memory NtUnmapViewOfSection() Unmap a section from memory NtQuerySection() Returns section size NtExtendSection() Change section size

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Using Shared Sections

Mapping unnamed Shared Sections. Need to know shared section handle on target process. Need permissions on target process.

OpenProcess(PROCESS_DUP_HANDLE,...)

DuplicateHandle(...)

MapViewOfFile(...)

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Using Shared Sections

Demo

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Tools

Process Explorer Shows information about processes (dlls, handles, etc.).

WinObj Shows Object Manager Namespace information (objects

info, permissions, etc.)

ListSS Lists Shared Sections names (local and TS sessions).

DumpSS Dumps Shared Section data.

TestSS Overwrites Shared Section data (to detect bugs)

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Problems

Input validation Weak permissions Synchronization

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Problems

Input validation Applications don't perform data validation before using the

data. Applications trust data on shared sections.

When applications read modified data from shared sections They will crash. They will perform unexpected actions.

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Problems

Weak permissions Low privileged users can access (read/write/change

permissions) shared sections on high privileged processes (services).

Terminal Services (maybe Citrix) users can access (read/write/change permissions) shared sections on local logged on user processes, services and also on other user sessions.

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Problems

Synchronization Not built-in synchronization. Synchronization must be done by processes in order to

not corrupt data. There isn't a mechanism to force processes to

synchronize or to block shared section access. Any process (with proper rights) can alter a shared

section data while another process is using it.

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Problems

Synchronization Communication between Process A and B

ProcessA

ProcessB

ProcessC

Shared Section

2- Write data.

3- Data ready.

4- Replace data.

5- Read data.

1- Send me data.

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Searching for holes

Look for shared sections using Process Explorer, WinObj or ListSS.

Attach a process using the shared section to a debugger.

Run TestSS on shared section. Interact with process in order to make it use

(read/write) the shared section. Look at debugger for crashes :).

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Searching for holes

Windows HTML Help Demo.

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Exploitation

Elevating privileges. Reading data. Altering data. Shared section exploits.

Using shared sections on virus/rootkits/etc.

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Exploitation

Reading data. From high privileged processes (services). From local logged on user processes, services and other

sessions on Terminal Services. This leads to unauthorized access to data.

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Exploitation

Altering data. On high privileged processes (services). On local logged on user processes, services and other

sessions on Terminal Services. This leads to arbitrary code execution, unauthorized

access, processes or kernel crashing (DOS).

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Exploitation

Shared section exploits. When overwriting shared section data allow us to take

control of code execution. Some shared sections start addresses are pretty static on

same OS and Service Pack. Put shellcode on shared section. Build exploit to jump to shellcode on shared section at

static location.

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Exploitation

Shared section exploits. MS05-012 - COM Structured Storage Vulnerability

Weak permission on shared section. Structures saved on shared section can be overwriten.

By overwriting these structures is possible to execute arbitrary code.

POC Exploit Demo.

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Exploitation

Using shared sections on virus/rootkits/etc. Some shared sections are used by many processes

(InternatSHData used for Language Settings on W2k) others sections are used by all processes :).

Write code to shared section and the code will be instantly mapped on processes memory and also on new created processes. Use SetThreadContext() or CreateRemoteThread() to start executing

code. Similar to WriteProcessMemory() - SetThreadContext() technique or

DLL Injection.

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Exploitation

Using shared sections on virus/rootkits/etc. Some shared sections have execute access.

It would be possible to avoid WinXP sp2 NX and third party protections.

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Microsoft vulnerabilities

Vulnerabilities on next Microsoft products have been reported and are being fixed: Internet Explorer vulnerability. Office vulnerabilities. Windows 2k and Windows XP sp2 Kernel vulnerability. IIS 5 vulnerabiliity. Windows COM vulnerability.

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Other vendors vulnerabilities

NOD32 antivirus vulnerability. Norton Antivirus (old versions) vulnerability. Veritas software vulnerabilities. Etc.

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Solutions

Set proper permissions Set only current user (also service account if application

running as service) permissions on shared sections unless another user should access them.

Use some synchronization mechanism Remember that when working with shared sections there

isn't built in synchronization.

Validate the data before using it Data on shared sections can be easily manipulated.

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Conclusions

Windows and 3rd. party applications have a bunch of Shared Section related holes.

These kind of holes will lead to new kind of attacks “SSAtacks” (Shared Section Attacks) ;)

Microsoft forgot to include a Shared Sections audit on the trustworthy computing initiative :).

Windows guts seem rotten:).

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References

MSDN Programming Applications for MS Windows - Fourth

Edition Process Explorer (www.sysinternals.com) WinObj (www.sysinternals.com) Rattle - Using Process Infection to Bypass Windows

Software Firewalls (PHRACK #62) Crazylord - Playing with Windows /dev/(k)mem

(PHRACK #59) http://www.microsoft.com/technet/security/bulletin/

MS05-012.mspx

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Briefing for:

FIN

• Questions?

• Thanks.

• Contact: cesar>at<argeniss>dot<com

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