Testing for Weak or unenforced username policy (OTG-IDENT-005)
This article is part of the new OWASP Testing Guide v4.
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User account names are often highly structured (e.g. Joe Bloggs account name is jbloggs and Fred Nurks account name is fnurks) and valid account names can easily be guessed.
Determine whether consistent account name structure renders the application vulnerable to account enumeration
Determine whether application's error messages permit account enumeration
How to test
Determine the structure of account names
Evaluate the application's response to valid and invalid account names
Use different responses to valid and invalid account names to enumerate valid account names
Use account name dictionaries to enumerate valid account names
Ensure the application returns consistent generic error messages in response to invalid account name, password or other user credentials entered during the login process.