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Testing for WS HTTP GET parameters/REST attacks (OWASP-WS-005)

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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

Many XML applications are invoked by passing them parameters using HTTP GET queries. These are sometimes known as “REST-style" Web Services (REST = Representational State Transfer). These Web Services can be attacked by passing malicious content on the HTTP GET string (e.g., extra long parameters (2048 chars), SQL statements/injection (or OS Injection parameters).

Description of the Issue

Given that REST Web services are in effect HTTP-In -> WS-Out, attack patterns, they are very similar to regular HTTP attack vectors, discussed throughout the guide. For example, in the following HTTP request with query string "/?viewDetail=detail-10293", the HTTP GET parameter is "detail-10293".

Black Box Testing and example

Say we had a Web Service which accepts the following HTTP GET query string: 

https://www.ws.com/accountinfo?accountnumber=12039475&userId=asi9485jfuhe92

The response would be similar to: 

<?xml version="1.0" encoding="ISO-8859-1"?>
<Account="12039475">
<balance>€100</balance>
<body>Bank of Bannana account info</body>
</Account>

Testing the data validation on this REST web service is similar to generic application testing:

Try vectors such as: 

https://www.ws.com/accountinfo?accountnumber=12039475' exec master..xp_cmdshell 'net user Vxr pass /Add&userId=asi9485jfuhe92


Grey Box Testing and example

Upon the reception of an HTTP request the code should do the following:

Check:

  1. Maximum and minimum length
  2. Validate payload
  3. If possible, implement the following data validation stratigies: "exact match", "known good" and "known bad", in this order.
  4. Validate parameter names and existence.

References

Withepapers

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