Owasp Forum Web Services Security

OWASP Top Ten Web Services Vulnerabilities Marco Morana OWASP Chapter Lead [email_address] Based upon Gunnar Peterson Presentation OWASP T10 Web Services Proposal OWASP USA 08 NYC Appsec Conference Cincinnati Chapter August 2009 Meeting

Meeting Agenda

Video Presentation: Web Services OWASP Top Ten Proposal by from Gunnar Peterson

http://video.google.com/videoplay?docid=5680040858618100893

Discussion Forum

Summary Of OWASP Top Ten For Web Services

Web Services Security Highlights

OWASP T10 Vulnerabilities

Issues

Countermeasures

Discussion Points: Q&A

OWASP References

Web Services Security Highlights

The security of web services and distributed architecture represents several challenges:

Security of the perimeter is not enough

Data segregation does not separate good from evil

Security goal cannot be limited to CIA attributes

Location independence : authenticate in one place and authorize in another place

Interoperability across systems and technologies

Consistent policy enforcement

Secure email vs. tiered architecture

Security of the delivery channel and the intermediaries

Design-time activity aimed at pointing out common security pitfalls and proper ways to implement security within design patterns

Originally a white paper – donated to OWASP by Security Compass

Web Services OWASP T1 Vulnerability

Injection Attacks

Issue highlights:

Larger attack surface and new targets for injection flaws: SQL injection, LDAP and XPATH/XQUERY, XSLT, HTML, XML, OS command injection

WS as gateway to inject data in backend services : mainframes, MQs, ESB, SAP

More attack vector opportunities: decoupling between web service requester and provider

Countermeasures:

Determine the application attack surface and the entry points

Validate at each trust boundary (front end, middleware, backend)

Input validation strategy: encoding, sanitization , canonicalization

Malicious file execution

Issue highlights:

Web service processing can take un-trusted input to inject system and backend commands and exploit it for remote command execution, upload malware or cause a denial/degradation of service

DOS via file upload and SOAP interface can be abused to cause denial or degradation of services (overload the XML parser)

Countermeasures:

Do not trust client supplied parameters for remote command execution, when uploading files, validate server side the file upload size, name, file path and the file extension/parameters

Validate XML size and XSD schema before processing

Insecure Object Reference

Issue highlights:

Abuse of object references lead to remote code execution

Failure to check data reference and URL parameters lead to remote root kit installation and compromise: Some cases banking applications use ACC# as PK that can be misused for SQL injection if is not validated

Countermeasures:

Use encryption and signatures to prevent tampering of SOAP messages, validate references on the server side

Beware of REST: some IDE add a REST call in form of a GET that can be called without authorization: this need to be turned off.

Information Leakage

Issue highlight:

Too much WS configuration information such as application type and methods used via WSDL readable to public, access to XSD and XML let the attacker know the data and the values to attack, the UDDI (the registry) can leak information such as addressing routing structure or behavior

Countermeasures:

Remove WSDL files from web server

Disable the documentation protocols to prevent dynamic generation of WSDL

Capture exceptions that return minimal information to the users

Broken Authentication And Weak Tokens

Issue highlights:

Tokens non protected as well as assertions, flaws allow to hijack user admin accounts, bypass authorizations and allow for reply attacks.

Claim based (SAML) access control vs. RBAC exposes the application to new vulnerabilities

Countermeasures:

Authentication via password digest, SAML and Kerberos tickets ,X509 certificates, Username and password in plaintext

SSL and message payload encryption for transit protection

Unique message ID, data stamp and nonce with each request to prevent message replay

Digital signature to prevent tampering

Insecure Crypto Usage

Issue highlights:

Not encrypting secrets and protecting keys

Use of weak crypto and non standard algorithms such as MD5 and RC3 and RC4

Hard-coding keys

Misuse of XML encryption: signature tag with no signature value, homegrown encryption algorithms

Countermeasures:

Protect secrets with encryption use secure key storage

Use standard secure cryptographic algorithms

Do not hardcode secrets

Do not use homegrown encryption implementations/schemes

Test your crypto implementation

Insecure communications

Issues highlights:

Not using SSL exposes authentication, sensitive and session data and sensitive info.

Sniffing attacks : WS and SAML tokens can be sniffed in transit with no SSL that protects them

Timing and replay attacks are possible for unprotected session data

Countermeasures:

Protect data in transit: SSL/IPsec

Protect XML documents/sections with XML encryptionValidate signatures properly (presence and who trusted it)

Failure to restrict access

Issue highlights:

Failure to enforce WS method authentication

Some web service methods use MQ listeners with no authentication to call them , attackers can exploit the gateway to mainframes and messaging systems (e.g. ESB)

Countermeasures:

Server to server and trusted authentication (SAML) across systems

Message level authentication (usr/pwd, kerberos, X509, SAML)

Application level auth (role-based authorization for methods)

Web Services OWASP T9 Vulnerability (New proposal)

Broken XML

Issue highlights:

WS rely on XML document binding based upon data parameters encoded and parsed that can be injected

Failure to validate parameters and well formed XML and XSD can lead to DOS

Recursive XMLs (DTD based) can lead to DOS

Injected CDATA elements (not interpreted) can fail the parser

Countermeasures:

Specify the XML size and schema via DTD for old SOAP (do not use DTD not allowed in current spec!) and XSD

Do not use old Xerces parser (prone to DOS)

Validate all input and encode output

Web Services OWASP T10 Vulnerability (New proposal)

Identity Misuse

Issue highlights:

The WS identity is the basis for WS claims and assertions for routing decisions ( to pass to different back end services), business logic and access control (authentication)

A mis-configured identity claim can be misused : A malicious service provider can have access to different services used by Google (token sent back was valid for any Google service) and other identity providers.