Subverting WCF Security [starting points]

1. Subverting WCF Security[starting points] Marc Schönefeld University of Bamberg

2. The speaker • Marc Schönefeld, Diplom-Wirtschaftsinformatiker • For Science: External doctoral student @ Lehrstuhl für praktische Informatik at University of Bamberg, Bavaria, Germany • Thesis project: REFACTORING OF SECURITY ANTIPATTERNS IN DISTRIBUTED JAVA COMPONENTS • For Living: Security Management for large financial group in Germany

3. WCF is part of NET 3.0 • NET 3.0 is • is the former WinFX ( Windows Framework Extension) • According to Microsoft Arithmetics, it is NET 2.0 plus • WPF (Presentation) aka Avalon • WCF (Communication) aka Indigo • WWF (Workflow) • available for Windows XP SP2, Windows Server 2003 and Windows Vista

4. WCF as part of NET 3.0

5. NET 3.0 is not a new .NET • .NET 3.0 is just a set of additional assemblies on top of .NET 2.0

6. WCF unifies Communication handling • Communication • WCF supports various existing communications and hosting runtime models • ASP.NET • COM+ • WSE • NET-Remoting • Pipes and Queues

7. WCF … • allows to publish .NET classes as services • import from services into .NET classes. • includes interoperability code to handle service protocols, type conversion and value marshaling. • Allows developers to easily connect their applications to web services.

8. WCF … • supports non-functional requirements (reliable calls, asynchronisity, transactionality, security) • comes with predefined adapters • can be extended with custom handlers for non-standard scenarios. • classes reside mostly in the System.ServiceModel namespace • is physically located in the System.ServiceModel.dll assembly.

9. WCF terms • SOA (Service oriented architectures) help the infrastructure to host local or remote services that can be used with clients. • Clients do not need to know the language, platform or version of the service. • Services provide functionality, can be newly written code or a decorated COM+ service • Clients use functionality provided by services, can be an ASP.NET page, Windows Form • Proxies decouple Services from Clients.

10. WCF supports local scenarios

11. WCF supports remote scenarios

12. WCF authentication and authentication • Authentication is about to determine the identity of the service caller: • Noauth Anonymous access is allowed • Windows Kerberos for Windows Domain or NTLM for workgroup (this is default) • UID+PWD Checks credentials against Windows accounts or database entries • X509 cert In a PKI environment the client authenticates with a known certificate • Secure Token Support a federated trust environment (WS-Trust) • Custom authentication Roll your authentication, in most cases not a good idea • WCF Authorization determines permissions of service caller by using • Windows Groups • ASP.NET provider (such as a databases)

13. Transports: Securing the wire • The goal is to maintain integrity and privacy of the message while in transit. Staged options available: • Transport Security • uses secure transport layer over TCP, HTTP, IPC, MSMQ • Message Security • encrypts the message • Mixed Transport and Message , • transport security secures privacy and integrity, message security secures client credentials, near to overkill • Both • First the message content secured by message security mechanisms additionally a secure transport is used. Almost always overkill

14. Service B Service A A A B B Address (Where) C C Binding (How) Contract (What) WCF separates Where, What and How Server Client A B C

15. Service Endpoints • Clients and Servers use Service Endpoints for WCF communication • Client communicates to 1-n server endpoints • Client may open an endpoint for duplex message exchange (DualHttpBinding) • Service Endpoints specify • Endpoint address: Where is the service • Binding: How to attach to the service • Contract: What is exchanged between client and server • Behavior: Extension of binding behavior

16. Endpoint URI Headers Header Identity Information Endpoint address (WHERE) • The Physical address of the Endpoint (like an URI) • Headers (Optional), needed when multiple servers share an URI • Identity information

17. Binding settings (HOW) • Name and namespace identify a service • Binding elements adjust communication details (reliability, SOAP message security, TCP layer protection) • Many presets Binding Name Namespace Binding Elements Bindings Element

18. WCF Contracts (WHAT) Contract • Name and namespace again identify a service • Operation Description determine the type (send/forget, request/reply) • Duplex operations talk back to the client Name Namespace Operation Description Set Operation Descr. Message Descr. Set Msg. Description Contract Behavior Set Contract Behavior

19. A Service description is the server config Service Description • A service is typed and has several behavior settings, • It can be reached on multiple endpoints (one on plain TCP, another one over HTTP, …) ServiceType Service Behavior Set Service Behavior Set of Service endpoints Service Endpoints Endpoint address Binding Contract

20. A Channel description is the client config Channel Description • A channel is used by the client and has several behavior settings, • It has one endpoint (one on plain TCP, another one over HTTP, …) Channel Behavior Set Channel Behavior Service Endpoints Endpoint address Binding Contract

21. WCF runtime environment concepts • Messages • Represented as a SOAP infoset, the message is the core part of information in WCF • its serialization format can be XML text, binary (for WCF2WCF) or a customizable format (JSON, XML-RPC) • Channels • Path to send a message send from Endpoint to endpoint, channels are layered • A Transport channel defines the media to send the physical data (UDP, MQ, Pipe, TCP) • A Protocol channels defines how to manipulate the data (like the SOAP protocol) • A security channel defines how to protect the message

22. WCF startup procedure • The server initializes a ServiceHost object and opens the endpoints (XML config  or hardcoded ) • The client initializes a ChannelFactory object (also in config or In code)

23. Intranet bindings • BasicHttpBinding • For ASMX-based Web services and clients and other services that conform to the WS-I Basic Profile 1.1 • Security is turned off by default • Text encoding, UTF-8 • NetTcpBinding • For secure for cross-machine communication • transport security • binary message encoding

24. Intranet bindings • NetPeerTcpBinding • Peer-2-Peer communication over TCP • Input, Output and Duplex channels • Transport security by default • NetNamedPipe • for on-machine communication • Transport security on by default • Pipename is Base64 encoded servicename

25. Internet bindings • WSHttpBinding • http binding for Web services features • message security • transactions, reliable messaging, and WS-Addressing secure and reliable binding • WSFederationHttp • Like WSHttpBinding but with SSO capabilities • Ideal choice for secure tokens (http://weblogs.asp.net/cibrax/archive/2006/03/14/440222.aspx)

26. Internet bindings • WSDualHttpBinding • Usable for service contracts in duplex mode allowing both services and clients to send and receive messages • supports only SOAP security and requires reliable messaging • NetMsmqBinding • support for transport on top of Microsoft Message Queuing (MSMQ) • For designing loosely coupled applications, failure isolation, load leveling and disconnected operations • In early versions there were DOS problems with msgs larger than 64K

27. Threat modeling: Integrity WCF & OWASP A1 Unvalidated Parameters A2 Broken Access Control A3 Broken Account and Session Management A4 Cross-Site Scripting (XSS) Flaws A5 Buffer Overflows A6 Command Injection Flaws A7 Error Handling Problems A8 Insecure Use of Cryptography A9 Remote Administration Flaws A10 Server Misconfiguration

28. WCF & OWASP • A1: Unvalidated parameters : • There is no protection against unvalidated parameters, there is no tainting model in .NET 3.0 • A4: XSS: • Therefore no support against XSS • A5: Buffer overflows • COM+ legacy code (in C/C++) can be overflowed, although connected via WCF • A6: Command injection: • Depends on how the application handles and propagates data flow of untrusted values into SQL parms • A10: Server Misconfiguration • Hard coded configurations in applications may lead to flaws, deployer personnel may be confused by the many options to choose from (where to set ciphersuite?)

29. Threat modeling: WCF & COM+ • WCF allows to integrate COM+ with the ComSvcConfig tool • Two hosting modes available for COM+ • COM+ default: The Component runs within DLLHOST • Web based: The component runs within IIS, activation with request • Beware that you don’t resurrect some old vulnerable components • Before deploying check the component!

30. Threat modeling: Confidentiality • In a threat modeling setup about communication we have • Alice wants to communicate with Bob, • Mallory wants to interfere • WCF protects us very good against wiretapping • Mallory sitting on the transport wire • WCF does not protect against interfering • Mallory sitting between Alice and her endpoint or Bob and his endpoint (like a patched CLR, application) • WCF does not protect against stolen credentials • Once Mallory has stolen/leaked the key and code from Alice she has full access

31. Threat modeling: Code security • WCF protects us against type confusion • by the use of strong contracts • Big advantage over Java serialisation • .NET protects against integer overflows • In contrast to java it alarms the flipping sign • XML parser seems to be quite stable • Against large message attacks • Against several XML anomalies attacks

32. Secure coding in WCF • Static code checking helps to find problem areas in own and third party code • Not all code is immediately accessible • Third party libraries may be encrypted or otherwise protected, so often a free tool from salamander helps to get the code out • http://www.remotesoft.com/deprotector/ • No Sourcecode is no Prob: MSIL binary has it all! • Despite a lot of false positives static MSIL checkers may help • FXCop is a good starting point, is free at http://www.gotdotnet.com/Team/FxCop • Comes with a set of predefined security rules !

33. Secure coding in WCF • Some Relevant FXCop secure coding guidelines, which are helpful when coding with WCF • Review imperative security • Review sql queries for security vulnerabilities • Pointers should not be visible • Do not indirectly expose methods with link demands • Do not declare read only mutable reference types • Aptca methods should only call aptca methods • Aptca types should only extend aptca base types • Code your own rules and alter existing ones: • http://weblogs.asp.net/pglavich/archive/2005/07/19/419869.aspx • http://www.futureware.biz/blog/index.php?title=writing_your_own_fxcop_rules_library

34. The wishlist • Better performance • WCF over XML is slow • WCF over XML + security is d**n slow (even on 3Ghz machine) • Remember: Availability is a security aspect ! • Home phoning issues • WCF wants to validate certificates and sends HTTP request to Microsoft • Better usage of Secure string implementation • Credentials are stored insecure in normal strings • It would be helpful to advise .NET to store directly data directly in SecureString fields after reception from a service • No patterns available, Developers are left alone • with finding the relevant mix of options • With adjusting protection level and performance

35. Summary • WCF delivers a new baseline security model. • Various deployment and configuration features allow subverting the default security model • Easiness of legacy (COM+) integration allows vulnerable code to be called in the backend • Secure coding is still a must, despite a secure transport framework

36. Q&A どうもありがとう Domo arigato marc.schoenefeld ät gmx dot org.ilasm