Active Debug Code

Description

A common development practice is to add "back door" code specifically designed for debugging or testing purposes that is not intended to be shipped or deployed with the product. These back door entry points create security risks because they are not considered during design or testing and fall outside of the expected operating conditions of the product.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

Debug code can be used to bypass authentication. For example, suppose an application has a login script that receives a username and a password. Assume also that a third, optional, parameter, called "debug", is interpreted by the script as requesting a switch to debug mode, and that when this parameter is given the username and password are not checked. In such a case, it is very simple to bypass the authentication process if the special behavior of the application regarding the debug parameter is known. In a case where the form is:

<FORM ACTION="/authenticate_login.cgi">
  <INPUT TYPE=TEXT name=username>
  <INPUT TYPE=PASSWORD name=password>
  <INPUT TYPE=SUBMIT>
</FORM>

Then a conforming link will look like:

http://TARGET/authenticate_login.cgi?username=...&password=...

An attacker can change this to:

http://TARGET/authenticate_login.cgi?username=&password=&debug=1

Which will grant the attacker access to the site, bypassing the authentication process.

See Also