Forced Password Reset? Check Your Assumptions
Almost weekly now I hear from an indignant reader who suspects a data breach at a Web site they frequent that has just asked the reader to reset their password. Further investigation almost invariably reveals that the password reset demand was not the result of a breach but rather the site’s efforts to identify customers who are reusing passwords from other sites that have already been hacked. But ironically, many companies taking these proactive steps soon discover that their explanation as to why they’re doing it can get misinterpreted as more evidence of lax security. This post attempts to unravel what’s going on here.
The reality is Facebook, Netflix and a number of big-name companies are regularly combing through huge data leak troves for credentials that match those of their customers, and then forcing a password reset for those users. Some are even checking for password re-use on all new account signups. The idea here is to stymie a massively pervasive problem facing all companies that do business online today: Namely, “credential-stuffing attacks,” in which attackers take millions or even billions of email addresses and corresponding cracked passwords from compromised databases and see how many of them work at other online properties.
So how does the defense against this daily deluge of credential stuffing work? A company employing this strategy will first extract from these leaked credential lists any email addresses that correspond to their current user base. From there, the corresponding cracked (plain text) passwords are fed into the same process that the company relies upon when users log in: That is, the company feeds those plain text passwords through its own password “hashing” or scrambling routine. If a user’s plain text password from a hacked database matches the output of what a company would expect to see after running it through their own internal hashing process, that user is then prompted to change their password to something truly unique.
I can’t stress this enough: Do not re-use passwords. And don’t recycle them either. Recycling involves rather lame attempts to make a reused password unique by simply adding a digit or changing the capitalization of certain characters. Crooks who specialize in password attacks are wise to this approach as well.