Testing for Code Injection (OTG-INPVAL-012)
This section describes how an attacker can enter code as input on a web page and have it executed by the web server.
Description of the Issue
Code Injection attacks involve an attacker submitting code as input that is processed by the web server as dynamic code or as in an included file. These attacks can target various server side scripting engines, i.e. ASP, PHP, etc. Proper validation and secure coding practices need to be employed to protect against these attacks.
Black Box testing and example
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:
The malicious url is accepted as a parameter for the PHP page, which will later use the value in an include file.
Gray Box testing and example
Testing for ASP Code Injection vulnerabilities
Examining ASP code for user input used in execution functions, e.g. Can the user enter commands into the Data input field? Here, the ASP code will save it to 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 %> <form> <input name="Data" /><input type="submit" name="Enter Data" /> </form> <% End If %>)))