Thick Application Penetration Testing: Crash Course

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This presentation will provide a high level overview of the current role that desktop applications play in enterprise environments, and the general risks associated with different deployment models. It will also cover common methodologies, techniques, and tools used to identify vulnerabilities in typical desktop application implementations. Although there will be some technical content. The discussion should be interesting and accessible to both operational and management levels.

More security blogs by the authors can be found @
https://www.netspi.com/blog/

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Thick Application Penetration Testing: Crash Course

  1. 1. Thick Application Penetration TestCRASH COURSE v1.0Author: Scott Sutherland
  2. 2. Who am I?Scott SutherlandPrincipal Security Consultant• Penetration Testing ‒ Networks ‒ Web apps / services ‒ Thick apps• Community Stuff ‒ Researcher ‒ Blogger ‒ Tool smith (or smithy if you like) ‒ Twitter stalker: @_nullbind
  3. 3. 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
  4. 4. Why am I talking about this?Thick applications create uniquerisks that web applications dont.
  5. 5. Why am I talking about this?Users often have full control over theapplication environment which: ‒ Allows attacks on trusted components ‒ Exposes data, admin/hidden functions ‒ Leads to application and OS privilege escalation
  6. 6. Why am I talking about this?Thick applications are the new web applications.
  7. 7. Why am I talking about this?Publishing thick applications via TerminalServices 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
  8. 8. Why am I talking about this?Publishing thick applications via TerminalServices and Citrix: Bad Stuff ‒Very hard to secure published desktops/applications ‒Commonly results in direct database access ‒Often exposes internal networks of service provider
  9. 9. Testing Goal & ObjectivesGoal:Determine what risks the application implementationpresents 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
  10. 10. Scoping ProjectsEstimate effort: ‒ Number of forms ‒ Number of files ‒ Number of registry keys ‒ Number of user levels ‒ Application architecture ‒ Application technology ‒ Constraints ‒ EnvironmentGenerally… ‒ More stuff = more time ‒ More complexity = more time
  11. 11. Common ArchitecturesDesktop Client  Remote Database ‒ Usually entire implementation is on internal networkDesktop 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 providerDesktop 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
  12. 12. Common ArchitecturesTerminal Services Application ‒ RDP  Terminal Server  Published app ‒ Website  RDP  Terminal Server  Published appCitrix Application ‒ Citrix client  Terminal Server  Published app ‒ Website  Citrix client  Published appThin Application ‒ VMware application ‒ Hyper-V application
  13. 13. 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
  14. 14. Testing RequirementsMinimum Requirements:• 2 application credentials for each role• Application AccessPotential Requirements:• VPN access• Local administrator on client test system• Internet endpoints• Installation package
  15. 15. Application Walkthrough• Verify connectivity to application• Verify all credentials• Walk through common use cases• Identify potential areas of client concern• Better understand application architecture
  16. 16. Application TargetsUNMANAGED CODE APPLICATIONS and MANAGED CODE APPLICATIONS
  17. 17. 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
  18. 18. 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
  19. 19. Attack VectorsThe usual suspects:• Application GUI • Network traffic• Files and folders • Application memory• Windows registry • Configurations
  20. 20. Application Test PlanCreate 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
  21. 21. 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
  22. 22. 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
  23. 23. 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
  24. 24. Testing the Application: GUI Tool DescriptionUISpy Enable disabled functions, and call actions related to disabled functions. Show hidden objects, enabled disabled objects, execution functions, and generallyWinCheat manipulate remote form objects. View form object properties including the value of masked password fields, and maskWindow Detective card numbers.
  25. 25. 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
  26. 26. 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
  27. 27. Testing the Application: Files Tool DescriptionAccessEnum, Privesc, autoruns, Dump file, registry, and service permissions. Also, review scheduled tasks excessive privilege and write scriptschtasks locations. .Net Reflector, Reflexil, ildasm, IL_Spy, Decompile or disassemble binaries to recover source code, IL code, or assembly code. Use code review tools toGraywolf,JD Java decompiler, java byte identify vulnerabilities, and review for sensitive data such as passwords, private keys, proprietary algorithms.code editor, Metasm, CFFExplorerReflexil .net reflector plugin, Graywolf De obfuscate decompiled assemblies Review exports, view/edit imports, edit and extract resources, view disk/memory usage to identify compression,CFF Explorer, dllexp disassemble binary, and finger print language MSFpayload. MSFencode, and MSFVenom can be used to generate shell code, DLL and EXE payloads forMetasploit injection and side loading. This also ships with METASM ruby library that can be used to disassemble and compile binariesProcess Explorer View image file settings, process, connections, threads, permissions, strings from process, environmental variables View DEP/ASLR settings, image file settings, process, connections, threads, permissions, strings from process,Process Hacker 2 environmental variablesProcess 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 expressionsStrings Dump strings from filesSymantec EPP Scan all files for know malwarePE Explorer Detect compiler or packer type and versionUPX, MPRESS, Iexpress, 7zip Decompress/unpack binaries and other filesVisual Studio, Ilasm, Metasm, winhex Edit exported .net reflector projects, IL, or assembly and create patched executables.
  28. 28. 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
  29. 29. Testing the Application: Registry Tool DescriptionTools:AccessEnum Dump file and registry permissionsRegedit Backup, review, and edit the registryRegshot Registry diffing tool.Process Monitor Monitors calls to file, registry keys, and sockets
  30. 30. 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
  31. 31. Testing the Application: Network Tool DescriptionCain 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 BURPWeb Inspect Service Attack Tool Generic web service review.Wireshark, windump, Dump all network traffic. Rawcap is the bomb.tcpdump,Rawcap
  32. 32. 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
  33. 33. Testing the Application: MemoryRun-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
  34. 34. Testing the Application: Memory Tool DescriptionMetasploit 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 variablesProcess Hacker 2 View image file settings, DEP/ASLR settings, connections, threads, permissions, environmental variables, inject DLLRemoteDLL Can be used to inject a DLL into a process.Tsearch Can be used to quickly find and replace strings in memory.Immunity, OllyDBG, Can be used to step through the application and modify assembly instructions on the fly.Windbg, and IDADebuggersWinhex Can be used to quickly find and replace strings in memory.Userdump Dump memory from process.
  35. 35. 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
  36. 36. Testing the Application: Configurations Tool Descriptionwindows-privesc- Check privileges on servers and associated program directories, and manuallycheck check for insecurely registered services.Citrix Client Used to connect to Citrix applications.Data Source (ODBC) Look for existing ODBC connection and use tools like excel to leverage them.Administrative ToolServices.msc, Review application services for insecure registration, binary paths, andwindows-privesc- determine users who is running the service.checkSQL Clients Used to connect directly to the database. Examples include OSQL, ISQL, SQLCMD, RAZOR SQL,TOAD, Microsoft SQL Management Studio Express.Windows Explorer and Access Windows dialog boxes to obtain access to a cmd console orcommon dialog boxes Powershell. Target links, shortcuts, open file functions, export functions, import functions, and reporting functions. Help menus and verbose error pages can also be handy.
  37. 37. Vulnerability Categories1. Application Logic2. Code Injection3. Excessive Privileges4. Unencrypted Storage of Sensitive Data5. Unencrypted Transmission of Sensitive Data6. Weak Encryption Implementations7. Weak Assembly Controls8. Weak GUI Controls9. Weak or Default Passwords
  38. 38. 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
  39. 39. 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

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