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Subverting WCF Security[starting points]: 

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

The speaker: 

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

WCF is part of NET 3.0: 

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

WCF as part of NET 3.0: 

WCF as part of NET 3.0

NET 3.0 is not a new .NET: 

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

WCF unifies Communication handling: 

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

WCF …: 

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.

WCF …: 

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.

WCF terms: 

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.

WCF supports local scenarios: 

WCF supports local scenarios

WCF supports remote scenarios: 

WCF supports remote scenarios

WCF authentication and authentication: 

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)

Transports: Securing the wire: 

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

WCF separates Where, What and How : 

WCF separates Where, What and How Client Server A B C

Service Endpoints: 

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

Endpoint address (WHERE): 

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

Binding settings (HOW): 

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

WCF Contracts (WHAT): 

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

A Service description is the server config: 

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

A Channel description is the client config: 

A Channel description is the client config 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 Description Service Endpoints Endpoint address Channel Behavior Set Channel Behavior Binding Contract

WCF runtime environment concepts: 

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

WCF startup procedure : 

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)

Intranet bindings: 

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

Intranet bindings: 

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

Internet bindings: 

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 (

Internet bindings: 

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

Threat modeling: Integrity WCF & OWASP : 

Threat modeling: Integrity WCF andamp; 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


WCF andamp; 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?)

Threat modeling: WCF & COM+ : 

Threat modeling: WCF andamp; 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!

Threat modeling: Confidentiality: 

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

Threat modeling: Code security: 

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

Secure coding in WCF: 

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 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 Comes with a set of predefined security rules !

Secure coding in WCF: 

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:

The wishlist: 

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

Summary : 

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


Qandamp;A どうもありがとう Domo arigato marc.schoenefeld ät gmx dot org.ilasm

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