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Web Services Security

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  1. Web Services Security Pete Lindstrom, CISSP Research Director Spire Security, LLC www.spiresecurity.com petelind@spiresecurity.com

  2. Agenda • Web Services Threat Profile • Top Ten Attacks • Defending Against the Top Ten Attacks • Conclusions

  3. Web Services Opportunities & Risks • Multiple data sources provide many alternatives and opportunities for business. • How do we ensure that the data sources are legitimate? • Real-time transactions can be submitted just-in-time. • How do we validate the data prior to its use? • Contextual data makes integration easy. • Who else may intercept the data? • Directories allow for dynamic lookups and immediate gratification. • How do we validate the directories?

  4. Web Services: Bane or Panacea? From monolithic mainframe, to two- and three-tier client server, to n-tier Web. Now, we have n-peer Web Services • Standardization: common communication protocols • Easier to learn technology, higher likelihood of finding a target. • Loose-coupling: flexible architecture • More uniquely addressable attack points. • Federation: working together • More ways to “hide” amidst legitimate traffic. Increased functionality brings increased risk, but it may be worth it.

  5. Web Services Components • XML/SOAP Communication protocols. • Configuration Data (the setup) • XML Processors • Legacy Apps • External Entities

  6. XML/SOAP Protocols • Protocol Abuse • XML Information as: • Protocol / Tags • Expected operations • RPC / Command (embedded code) • And variables, flags, attributes • Data/transaction • URIs - pointers

  7. Web Services Configuration Data • Web Services Description Language (WSDL) Files • XML Schemas • XSLT Files • WS-Policy information

  8. XML Processor • Standard operations • Parse XML • Aggregate data • Transform data • Canonicalize data • All Legitimate manipulation of data after the source. • Legacy bolt-ons • Untrusted entities

  9. External Entities Local/UDDI Format/C14N Schema WSDL WS-Policy XSLT XML Route/Switch XML Processor Applications .Net/J2EE Protocol Conversations Legacy Apps Program Instructions Parse, Evaluate, Transform Web Services Consumer Methods and Bindings Repositories Transactions XML-DB File Systems RDBMS XML Documents Web Services Threat Profile

  10. Data Protection Goals • Confidentiality – protect data from being seen by inappropriate people/entities. • Integrity – protect data from being modified inappropriately. • Authenticity – ensure the data and its source are legitimate. • Availability – ensure the data is accessible by appropriate entities.

  11. Basic Confidentiality Encryption: • Encrypt data with symmetric key • Securely transfer key to recipient (e.g. encrypt symmetric key with recipient’s public key) Decryption: • Securely receive key (e.g. decrypt symmetric key with recipient’s private key) • Decrypt data with symmetric key

  12. XML Encryption • Candidate Recommendation • How to represent encrypted data within XML • Separate encrypted data from encryption information • Super-encryption • http://www.w3.org/Encryption/2001/

  13. XML Encryption Elements • <EncryptedData> container element • <EncryptionMethod> element: describes the encryption algorithm. • <KeyInfo> element: defined in XML-DSIG • <CipherData> envelopes or references raw encrypted data • <CipherValue> raw data if enveloped • <CipherReference> reference data if detached

  14. XML Encryption Encryption: • Use <EncryptionMethod> to create <CipherValue> described by <CipherData> elements. • Securely transfer key to recipient using <KeyInfo> or out of band method. Decryption: • Retrieve key using <KeyInfo>. • Take <CipherValue> and identify <EncryptionMethod> to decrypt data.

  15. XML Encryption Scenarios • Encrypt XML Element • Encrypt Element and Content • Encrypt XML Content (Character Data) • Encrypt Arbitrary Data and XML Documents • Super-encryption

  16. XML Encryption - Example Unencrypted Data <?xml version='1.0'?> <PaymentInfo xmlns='http://example.org/paymentv2'> <Name>John Smith</Name> <CreditCard Limit='5,000' Currency='USD'> <Number>4019 2445 0277 5567</Number> <Issuer>Example Bank</Issuer> <Expiration>04/02</Expiration> </CreditCard> </PaymentInfo> 1 2 3 4 5 6 7 8 9 Source: XML Syntax and Processing http://www.w3.org/TR/2002/CR-xmlenc-core-20020304/

  17. XML Encryption - Example Encrypting an XML Element (<CreditCard>) <?xml version='1.0'?> <PaymentInfo xmlns='http://example.org/paymentv2'> <Name>John Smith</Name> <EncryptedData Type='http://www.w3.org/2001/04/xmlenc#Element' xmlns='http://www.w3.org/2001/04/xmlenc#'> <CipherData> <CipherValue>A23B45C56</CipherValue> </CipherData> </EncryptedData> </PaymentInfo> 1 2 3 9 Source: XML Syntax and Processing http://www.w3.org/TR/2002/CR-xmlenc-core-20020304/

  18. XML Encryption - Example Encrypting XML Elements and Content (<number>; <issuer>; <expiration>) <?xml version='1.0'?> <PaymentInfo xmlns='http://example.org/paymentv2'> <Name>John Smith</Name> <CreditCard Limit='5,000' Currency='USD'> <EncryptedData xmlns='http://www.w3.org/2001/04/xmlenc#' Type='http://www.w3.org/2001/04/xmlenc#Content'> <CipherData> <CipherValue>A23B45C56</CipherValue> </CipherData> </EncryptedData> </CreditCard> </PaymentInfo> 1 2 3 4 8 9 Source: XML Syntax and Processing http://www.w3.org/TR/2002/CR-xmlenc-core-20020304/

  19. Encrypting XML Content (number itself) XML Encryption - Example 1 2 3 4 5 <?xml version='1.0'?> <PaymentInfo xmlns='http://example.org/paymentv2'> <Name>John Smith</Name> <CreditCard Limit='5,000' Currency='USD'> <Number> <EncryptedData xmlns='http://www.w3.org/2001/04/xmlenc#' Type='http://www.w3.org/2001/04/xmlenc#Content'> <CipherData> <CipherValue>A23B45C56</CipherValue> </CipherData> </EncryptedData> </Number> <Issuer>Example Bank</Issuer> <Expiration>04/02</Expiration> </CreditCard> </PaymentInfo> 5 6 7 8 9 Source: XML Syntax and Processing http://www.w3.org/TR/2002/CR-xmlenc-core-20020304/

  20. XML Encryption - Example Encrypt Everything 1 <?xml version='1.0'?> <EncryptedData xmlns='http://www.w3.org/2001/04/xmlenc#' MimeType='text/xml'> <CipherData> <CipherValue>A23B45C56</CipherValue> </CipherData> </EncryptedData> Source: XML Syntax and Processing http://www.w3.org/TR/2002/CR-xmlenc-core-20020304/

  21. XML Encryption Roundup • The goal is confidentiality (privacy). • The key is the key – key management. • Must be able to retain keys over time. • Must be able to protect the keys. • Must keep the key and the cipherdata separate.

  22. Integrity & Authenticity Sign: • Process data through one way hash • Sign hash with source private key • Transmit data Validate: • Validate signature with source public key • Re-hash data and compare

  23. XML Signature • RFC 3275, March 2002 • Works with any data object • Sign data in same XML document • Enveloped signatures (signature is child) • Enveloping signatures (signature is parent) • Sign data that is external to signature

  24. <Signature> </ Signature> <SignedInfo> </SignedInfo> <CanonicalizationMethod /> <SignatureMethod /> <Reference> </Reference> <Transforms> <DigestMethod> <DigestValue> <SignatureValue /> <KeyInfo /> XML Signature Container Format Data Signature Algorithm Hash Algorithm Hash Value Signed Hash Info Key Information

  25. XML Signature Elements • <Signature> element: Root • <SignedInfo> element: Container for signature information. • <C14NMethod> element: Algorithm used to format data prior to signing. [XML-C14N] • <SignatureMethod> element: Algorithm used to sign the hash (DSA-SHA1; RSA-SHA1)

  26. XML Signature Elements (cont’d) • <Reference> container for signatures. • <Transforms> describes processing requirements prior to sign/validate. • <DigestMethod> algorithm used to create hash. • <DigestValue> the hash itself • <SignatureValue> the operational results of signing the hash. • <KeyInfo> information on how to retrieve the validation key.

  27. XML Signature Sign: • Canonicalize data (<CanonicalizationMethod>) • Process data through one way hash (<DigestMethod>; <DigestValue>) • Sign hash with source private key (<SignatureMethod>; <SignatureValue>) • Transmit data Validate: • Validate signature with source public key • Re-hash data and compare

  28. Manifests • “Once-removed” signature. Validate the signed signatures. • Useful for performance considerations. • Provides selective validation. • Gotcha: individual signature validation must then occur within the application. • Individual signatures are not validated by xml signature.

  29. XML Signature Roundup • Always include dynamic information in signed data. • Protect against replay attacks. • Retrieve key info out-of-band. • Validate all algorithm sources.

  30. Transaction Attack Methods

  31. Sniff Modify Spoof Replay Transaction Security

  32. Authentication & Access Control On the user side: • Authentication validates the identity of the credential owner. • Access control maps an entity to its corresponding attributes (e.g. roles, group membership, etc.) On the resource side: • Describes under what conditions an entity is allowed to access a particular resource. • e.g. user name, group membership, time of day, etc.

  33. Security Assertion Markup Language (SAML) • OASIS Committee Specification • Assertions about authentication • Assertions about attributes • Assertions about authorization decisions • http://www.oasis-open.org/committees/security/

  34. SAML

  35. SAML Bindings and Profiles Binding • SOAP over HTTP Profiles • Browser/Artifact Profile (URL Query) • Browser/POST Profile (Form) • Replaces cookies

  36. SAML Roundup • Web Services Implementation • Session-based Protocol • Basic usage model: Single Sign-on • Useful for existing web and legacy apps

  37. XML Access Control Markup Language (XACML) • Rule • Target, Effect, Condition • Policy Statement • Multi-rule, Target, Obligations • Policy Set Statement • Multi-policy, Target, Obligations

  38. XACML • PAP – Policy Administration Point • PRP – Policy Retrieval Point • PEP – Policy Enforcement Point • PDP – Policy Decision Point • PIP – Policy Information Point

  39. XACML Policy Enforcement Point (PEP) Policy Decision Point (PDP) Policy Retrieval Point (PRP) Policy Information Point (PRP) Policy Administration Point (PAP)

  40. XACML • PAP – PRP: define policy. (admin action) • PEP – PDP: initial request and final decision. • PDP: Reconciles SAML assertions and XACML policy info. (next-gen firewalls?) • Takes request from PEP, policy from PRP, and attributes from PIP.

  41. XACML Roundup • Not ready for primetime, but… • Vendors have always had this capability in native apps. • Will standardize ACL models. • Can (potentially) replace native models. • Great for interchange of rules/policies.

  42. SAML - XACML SAML Assertions XACML

  43. Security “Specifications” WS- Secure Conversation WS-Federation WS-Authorization WS-Policy WS-Trust WS-Privacy WS-Security SOAP Foundation

  44. WS-Security • Message Integrity • Message Confidentiality • Message Authentication • Associated Security Tokens • Encoded Binary Security Tokens

  45. Follow-on Specs • WS-Policy: How senders and receivers specify capabilities and requirements. • WS-Trust: Establish direct and brokered trust. • WS-Privacy: State privacy policies and adhere to them. • WS-Secure Conversation: How to establish keys. • WS-Federation: How to link trust models. • WS-Authorization: How access policies are specified and managed.

  46. Agenda • Web Services Threat Profile • Top Ten Attacks • Note: These are primarily THEORETICAL attacks! • Defending Against the Top Ten Attacks • Conclusions

  47. 1. XML Encapsulation • Attacks legacy bolt-on XML processors. • External operation of normally local functions. • Uses “CDATA” feature in XML to “tunnel” through to app.

  48. XML Encapsulation Example <?xml version="1.0"?><?xml-stylesheet type="text/xsl" href="#?m$ux" ?><xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl"><xsl:script><![CDATA[x=new ActiveXObject("WScript.Shell");x.Run("%systemroot%\\SYSTEM32\\CMD.EXE /C DIR C:\\ /a /p /s");]]></xsl:script><msux>msuxwritten by georgi guninski</msux></xsl:stylesheet> Source: http://www.guninski.com/ex$el2.html

  49. 2. Coercive Parsing • Attacks legacy bolt-on XML processors. • Attacks old targets in new ways. • External operation of normally local functions. • Instead of using CDATA, uses XML parsing capability.

  50. 3. Recursive Elements • Use XML within a document to reference another point in the document. • Infinite loop