Testing for WS HTTP GET parameters/REST attacks (OWASP-WS-005)
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 Web services REST are in effect HTTP-In -> WS-OUT at attack patterns 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:
The resultant 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 a HTTP request the code should do the following:
- max length and minimum length
- Validate payload:
- If possible implement the following data validation stratigies; "exact match", "known good" and "known bad" in that order.
- Validate parameter names and existance.
- The OWASP Fuzz vectors list - http://www.owasp.org/index.php/OWASP_Testing_Guide_Appendix_C:_Fuzz_Vectors
OWASP Testing Guide v2
Here is the OWASP Testing Guide v2 Table of Contents