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OWASP Code Review Guide Table of Contents


The following discusses aspects of source code relating to weak authentication functionality. This could be due to flawed implementation or broken business logic: Authentication is a key line of defence in protecting non-public data, sensitive functionality

Weak Passwords and password functionality

Password strength should be enforced upon a user setting/selecting ones password. Passwords should be complex in composition. Such checks should be done on the backend/server side of the application upon an attempt to submit a new password.

Bad Example

Simply checking that a password is not NULL is not sufficient:

String password = request.getParameter("Password");
if (password == Null) 
   {throw InvalidPasswordException()

Good Example

Passwords should be checked for the following composition or a variance of such

at least: 1 Upper character (A-Z)
at least: 1 Lower character (a-z)
at least: 1 digit (0-9)
at least one special character (!"£$%&...)
a defined minimum length (8 chars)
a defined maximum length (as with all external input)

no contiguous characters (123abcd)
not more than 2 identical characters in a row (1111)

Such rules should be looked for in code and used as soon as the http request is received. The rules can be complex RegEx expressions or logical code statements:

if password.RegEx([a-z])
   and password.RegEx([A-Z])
   and password.RegEx([0-9])
   and password.RegEx({8-30})
   and password.RexEX([!"£$%^&*()])
   return true;
return false;


Vulnerabilities related to authentication

There are many issues relating to authentication which utilises form fields. Inadequate field validation can give rise to the following issues:

SQL injection can be sued to bypass authentication functionality and even add a malicious user to a system for future use.
Data validation of all external input must be performed. This also goes for authentication fields.
Cross site scripting can be used on the authentication page to perform identity theft, Phishing, and session hijacking attacks
Bad/weak error handling can be used to establish the internal workings of the authentication functionality such as giving insight into the database structure, insight into valid and invalid user ID's etc