Thick Application Penetration Test CRASH COURSE v1.0

Author: Scott Sutherland

Who am I?

Scott Sutherland Principal Security Consultant

• Penetration Testing

‒ Networks

‒ Web apps / services

‒ Thick apps

• Community Stuff

‒ Researcher

‒ Blogger

‒ Tool smith (or smithy if you like)

‒ Twitter stalker: @_nullbind

What are we going to talk about?

• Why should you care

• Testing Goal and Objectives

• Project Scoping

• Common Architectures

• Accessing the Application

• Testing Requirements

• Application Walkthrough

• Managed vs. Unmanaged

• Testing the Application

• Vulnerability Categories

• Reporting

Why am I talking about this?

Thick applications create unique risks that web applications don't.

Why am I talking about this?

Users often have full control over the application environment which:

‒ Allows attacks on trusted components

‒ Exposes data, admin/hidden functions

‒ Leads to application and OS privilege escalation

Why am I talking about this?

Thick applications are the new web applications.

Why am I talking about this?

Publishing thick applications via Terminal Services and Citrix: Good Stuff

‒ Helps meet client demand for “cloud services”

‒Converts Client/Server model to SaaS model

‒Cheaper/Faster than developing actual web based solution from scratch

Why am I talking about this?

Publishing thick applications via Terminal Services and Citrix: Bad Stuff

‒Very hard to secure published desktops/applications

‒Commonly results in direct database access

‒Often exposes internal networks of service provider

Testing Goal & Objectives

Goal:

Determine what risks the application implementation presents to the business so they can be mitigated.

Objectives:

Identify vulnerabilities that may exist in: ‒ The client application and server components

‒ The workstation or published application configuration

‒ The server or network configuration

Scoping Projects

Estimate effort: ‒ Number of forms

‒ Number of files

‒ Number of registry keys

‒ Number of user levels

‒ Application architecture

‒ Application technology

‒ Constraints

‒ Environment

Generally… ‒ More stuff = more time

‒ More complexity = more time

Common Architectures

Desktop Client Remote Database ‒ Usually entire implementation is on internal network

Desktop Client local DB Remote Database ‒ Local db typically syncs with remote db

‒ Usually client and local db are on internal network remote db is hosted by service provider

Desktop Client Application Server Database ‒ Usually client in on internal network and app/db server

is located is hosted by service provider

‒ Common technologies: Web Services, Web Applications, JBOSS, and IBM WebSphere

Common Architectures

Terminal Services Application ‒ RDP Terminal Server Published app

‒ Website RDP Terminal Server Published app

Citrix Application ‒ Citrix client Terminal Server Published app

‒ Website Citrix client Published app

Thin Application ‒ VMware application

‒ Hyper-V application

Accessing the Application

• Install locally, and test over VPN

• Install locally, and test over the internet

• Test over VPN, RDP to a client system, and install the tool sets for testing

• VPN + Terminal Services (TS)

• Web based TS

• VPN + Citrix Client

• Web based Citrix

• Run from network share

Testing Requirements

Minimum Requirements:

• 2 application credentials

for each role

• Application Access

Potential Requirements:

• VPN access

• Local administrator

on client test system

• Internet endpoints

• Installation package

Application Walkthrough

• Verify connectivity to application

• Verify all credentials

• Walk through common use cases

• Identify potential areas of client concern

• Better understand application

architecture

Application Targets

UNMANAGED CODE APPLICATIONS and

MANAGED CODE APPLICATIONS

UNMANAGED CODE APPLICATIONS

• General Information ‒ C and C++ (“unmanaged” or “native” languages) ‒ Compiled to machine code ‒ Include exportable functions

• Pros ‒ Typically run faster due to pre compiled code ‒ Can’t be easily decompiled to the original source code

• Cons ‒ Architecture specific ‒ Disassembly and reassembly is still possible ‒ API hooking is still possible

MANAGED CODE APPLICATIONS

• General Information ‒ Frameworks: .net (C# VB), Java Runtime, Dalvik ‒ Compiled to bytecode ‒ Usually does not include exportable functions ‒ Uses reflection to share public functions

• Pros ‒ Architecture independent ‒ Can be coded in different languages ‒ Can access unmanaged/native code

• Cons ‒ Slower due to Just in Time (JIT) compiling ‒ Disassembly and reassembly of CIL code is still possible ‒ Decompiling via reflection is still possible ‒ Global Assembly Cache (GAC) poisoning is possible ‒ API hooking is still possible

Attack Vectors

The usual suspects:

• Network traffic

• Application memory

• Configurations

• Application GUI

• Files and folders

• Windows registry

Application Test Plan

Create a test plan and follow it…

• Address high priority test cases identified by clients and business owners first

• Testing can be broken out by vector:

‒ GUI Review

‒ File Review

‒ Registry Review

‒ Network Review

‒ Memory Review

‒ Configuration Review

How far do we take this?

Stay in scope!

• That means only networks, servers, and applications defined by the client

• On in scope systems: ‒ Application admin = yes

‒ Database user = yes

‒ Database admin = yes

‒ Local OS admin = yes

‒ Remote OS admin = yes

‒ Domain Admin = yes

(IF logged into system)

…then no more escalation

Testing the Servers

• Automated authenticated scanning ‒ Multiple tools

‒ Multiple rounds

• Manual testing using standardized penetration test approach ‒ Information Gathering

‒ Vulnerability Enumeration

‒ Penetration

‒ Escalation

‒ Evidence Gathering

‒ Clean up

Testing the Application: GUI

• GUI object privileges Show hidden form objects Enable disabled functionality Reveal masked passwords (GUI B GONE)

• GUI content Review for sensitive data and passwords

• GUI logic Bypass controls using intended GUI Functionality Common Examples:

‒ SQL query windows ‒ Access control fields ‒ Export functions allow more access to data ‒ Break out of Citrix and Terminal Server applications ‒ External program execution

Testing the Application: GUI

Tool Description UISpy Enable disabled functions, and call actions related to disabled functions.

WinCheat Show hidden objects, enabled disabled objects, execution functions, and generally

manipulate remote form objects.

Window Detective View form object properties including the value of masked password fields, and mask

card numbers.

Testing the Application: Files

• File permissions Files and folders

• File Integrity Strong naming, Authenticode signing • File content Debugging Symbols/files, sensitive data, passwords, and settings

• File and content manipulation Backdoor the framework DLL pre loading Race conditions Replacing files and content

Common Examples:

‒ Application settings ‒ Trusted paths and executables ‒ Trusted hosts ‒ Update servers ‒ Passwords and Private keys

Testing the Application: Files

• Exported Functions (usually native code)

Identify and run exported functions without authenticating

• Public Methods (managed code reflection)

Create a wrapper to access public methods without authenticating

• Decompile and Recompile

Recover source code, passwords, keys, and create patched assembly

• Decrypt and Deobfuscate Recover source code, passwords, keys, etc

• Disassemble and Reassemble Create patched assembly

Testing the Application: Files Tool Description

AccessEnum, Privesc, autoruns, schtasks

Dump file, registry, and service permissions. Also, review scheduled tasks excessive privilege and write script

locations.

.Net Reflector, Reflexil, ildasm, IL_Spy, Graywolf,JD Java decompiler, java byte code editor, Metasm, CFFExplorer

Decompile or disassemble binaries to recover source code, IL code, or assembly code. Use code review tools to

identify vulnerabilities, and review for sensitive data such as passwords, private keys, proprietary algorithms.

Reflexil .net reflector plugin, Graywolf De obfuscate decompiled assemblies

CFF Explorer, dllexp Review exports, view/edit imports, edit and extract resources, view disk/memory usage to identify compression,

disassemble binary, and finger print language

Metasploit MSFpayload. MSFencode, and MSFVenom can be used to generate shell code, DLL and EXE payloads for

injection and side loading. This also ships with METASM ruby library that can be used to disassemble and

compile binaries

Process Explorer View image file settings, process, connections, threads, permissions, strings from process, environmental

variables

Process Hacker 2 View DEP/ASLR settings, image file settings, process, connections, threads, permissions, strings from process,

environmental variables

Process Monitor, API Monitor Monitors calls to file, registry keys, and sockets. API monitor does what it sounds like.

Spider2008 Search file system for interesting strings with regular expressions

Strings Dump strings from files

Symantec EPP Scan all files for know malware

PE Explorer Detect compiler or packer type and version

UPX, MPRESS, Iexpress, 7zip Decompress/unpack binaries and other files

Visual Studio, Ilasm, Metasm, winhex Edit exported .net reflector projects, IL, or assembly and create patched executables.

Testing the Application: Registry

• Registry permissions Read and write access to registry keys

• Registry content Sensitive data, passwords, and settings

• Registry manipulation Bypass authentication and authorization Replace content

Common Examples: ‒ Application settings

‒ Trusted paths and executables

‒ Trusted hosts

‒ Update servers

‒ Passwords

‒ Private keys

Testing the Application: Registry

Tools:

Tool Description

AccessEnum Dump file and registry permissions

Regedit Backup, review, and edit the registry

Regshot Registry diffing tool.

Process Monitor Monitors calls to file, registry keys, and sockets

Testing the Application: Network

• Network Rules Local and network firewall rules

• Network content Sensitive data, files, passwords, and settings

• Network manipulation Bypass authentication and authorization (SQL) Replacing content (Parameters)

Common Examples: ‒ Application settings ‒ Trusted paths and executables ‒ Trusted hosts ‒ Update servers ‒ Passwords ‒ Private keys

• Reverse and Fuzz Proprietary Protocols

Testing the Application: Network

Tool Description

Cain Can be used for ARP based man in the middle attacks. Can be used to parse password in live traffic or a pcap file.

Burp Can be used to manipulate HTTP traffic.

Metasploit Create custom fuzzer for RPC protocols.

Sully Create custom fuzzing templates.

Echo Mirage Generic TCP proxy.

Ettercap Can be used for man in the middle attacks. Can be used to modify traffic in transit with filters.

Evilgrade, interceptor-ng Tool for delivering Metasploit payloads instead of legitimate updates.

Network Miner Parse network traffic for files, systems, and shares.

oSpy, API Monitor 2 Dump data like encrypted SSL traffic and connection strings when DLL calls are made.

SOAPUI Can be used to interact directly with web services, and is often used with BURP

Web Inspect Service Attack Tool Generic web service review.

Wireshark, windump, tcpdump,Rawcap

Dump all network traffic. Rawcap is the bomb.

Testing the Application: Memory

• Process controls DEP, ASLR, permissions, and privileges

• Memory content Sensitive data, passwords, and settings

• Memory manipulation Bypass authentication and authorization Replacing content Common Examples:

‒ Application settings ‒ Trusted paths and executables ‒ Trusted hosts ‒ Update servers ‒ Passwords ‒ Private keys

Testing the Application: Memory

Run-time Modifications

• Direct editing

• DLL injection

• Shell code Injection

• Process replacement

• Modify assembly in memory

• Identification of dangerous functions

• Check if debugger can be run

• Debugging via stepping and breakpoints to analyze and modify

Testing the Application: Memory

Tool Description

Metasploit Can be used to generate shell code, exe, and DLL payloads. Can also be used to

migrate into a running process.

Process Explorer View image file settings, process, connections, threads, permissions, strings from

process, environmental variables

Process Hacker 2 View image file settings, DEP/ASLR settings, connections, threads, permissions,

environmental variables, inject DLL

RemoteDLL Can be used to inject a DLL into a process.

Tsearch Can be used to quickly find and replace strings in memory.

Immunity, OllyDBG, Windbg, and IDA Debuggers

Can be used to step through the application and modify assembly instructions on the

fly.

Winhex Can be used to quickly find and replace strings in memory.

Userdump Dump memory from process.

Testing the Application: Configurations

• Application user privileges

• Service account privileges

• Service configuration privileges

• Service registration

• Database account privileges

• Remote share permissions

• TS breakouts to OS

• Citrix breakouts to OS

Testing the Application: Configurations

Tool Description

windows-privesc-check

Check privileges on servers and associated program directories, and manually

check for insecurely registered services.

Citrix Client Used to connect to Citrix applications.

Data Source (ODBC) Administrative Tool

Look for existing ODBC connection and use tools like excel to leverage them.

Services.msc, windows-privesc-check

Review application services for insecure registration, binary paths, and

determine users who is running the service.

SQL Clients Used to connect directly to the database. Examples include OSQL, ISQL,

SQLCMD, RAZOR SQL,TOAD, Microsoft SQL Management Studio Express.

Windows Explorer and common dialog boxes

Access Windows dialog boxes to obtain access to a cmd console or

Powershell. Target links, shortcuts, open file functions, export functions,

import functions, and reporting functions. Help menus and verbose error

pages can also be handy.

Vulnerability Categories

1. Application Logic

2. Code Injection

3. Excessive Privileges

4. Unencrypted Storage of Sensitive Data

5. Unencrypted Transmission of Sensitive Data

6. Weak Encryption Implementations

7. Weak Assembly Controls

8. Weak GUI Controls

9. Weak or Default Passwords

Reporting Stuff

• Create severity ranking system based on static criteria

• Internally, criteria should take compensating controls into consideration

• Prioritize findings based on

ranking system

• Include instructions or

screen shots to help

reproduce and fix issues

• Don’t forget recommendations

Wrap Up

• General Summary ‒ Attack thick applications and related infrastructure

from many vectors using many tools

‒ Managed code suffers from inherent weaknesses that can’t be fixed and is easier to attack

• General Advice ‒ Never store sensitive anything in an assembly

‒ If something sensitive “must” be stored in an assembly use unmanaged coding languages like C and C++

‒ Be very careful to implement sufficient controls when deploying thick applications via terminal services or Citrix