That news follows Twitter's Friday disclosure of a security breach affecting an estimated 250,000 of its 250 million users. Following the breach, Twitter reset passwords for all affected users but said its related investigation -- including identifying exactly what data attackers accessed -- remains underway.
"This week, we detected unusual access patterns that led to us identifying unauthorized access attempts to Twitter user data," said Bob Lord, Twitter's director of information security, in a Friday blog post.
So far, however, it's not clear exactly what the attackers may have accessed. "We discovered one live attack and were able to shut it down in process moments later," Lord said. "However, our investigation has thus far indicated that the attackers may have had access to limited user information -- usernames, email addresses, session tokens and encrypted/salted versions of passwords -- for approximately 250,000 users."
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To err on the side of caution, Lord said passwords for those 250,000 users had been reset and that they should have received an email from Twitter telling them to create a new password. "As a precautionary security measure, we have reset passwords and revoked session tokens for these accounts," he said. "Your old password will not work when you try to log in to Twitter." Lord also urged users to pay attention to recently issued warnings from the Department of Homeland Security that using any version of the Java browser plug-in should be avoided unless absolutely necessary. But Lord said nothing that explicitly tied the breach of Twitter's system to an exploit of a Java vulnerability.
The ease with which attackers in possession of Twitter users' passwords can gain access to those users' accounts and to all private communications using Twitter appears to have driven company officials to begin pursuing two-factor authentication. This was revealed by a job listing on Twitter's site for a software engineer--product security. Listed in the job description is the responsibility to "design and develop user-facing security features, such as multifactor authentication and fraudulent login detection."
The job listing was spotted Monday by Britain's Guardian newspaper. Twitter didn't immediately respond to an emailed request for comment about whether it planned to add two-factor authentication to the site, or when it might make such a feature available. But Twitter's apparent two-factor authentication plans have already drawn praise. "This is a splendid idea -- I'm looking forward to it. It's something that we've wanted for some time," Graham Cluley, senior technology consultant at Sophos, told the Guardian. "We've often said we would be prepared to pay for it -- Twitter could monetize it by offering it to corporations and branded accounts. It would be pretty attractive."
Twitter's last major user-facing security improvement came in March 2012, when HTTPS became the default option for connecting to the site, thus securing communications between the Twitter site and Twitter users. Two-factor authentication, meanwhile, would add an extra layer of defense to Twitter's log-in processes and help stop attackers who managed to hack into Twitter's systems and steal users' passwords from accessing users' accounts.
Two-factor authentication has long been offered by Google for use with Gmail and other Google Apps. Dropbox, meanwhile, began offering two-factor authentication after suffering an embarrassing password breach. For both Google and Dropbox, users who have enabled two-factor authentication must enter both their password and a unique code -- the second factor -- generated either by an app on their smartphone or sent to their mobile phone in an SMS message.
Until Twitter adopts such a system, its only recourse when attackers hack into its systems and steal users' passwords -- assuming that the company spots the breach -- is to immediately expire those passwords, as Twitter says it has done. Interestingly, however, some affected users have reported that their expired passwords still work when they log into Twitter via the Twitter API, which is used by third-party tools such as Tweetdeck as well as Twitter's own iOS Twitter apps to allow the application to access Twitter.
According to Twitter spokesperson Jim Prosser, the continuing access comes via Twitter's use of the Open Authorization (OAuth) open source standard for authorization. "TweetDeck and other clients use OAuth, so as long as you don't sign out, you don't have to re-input your credential every time you open the app," Prosser told The Register, which first spotted the problem. But Twitter's failing to expire OAuth tokens means that not all users affected by the breach have had their OAuth session tokens likewise expired.
Twitter didn't immediately respond to an emailed request for comment about whether it might expire the OAuth tokens for users affected by the password breach.
This isn't the first seeming glitch in how Twitter handles third-party authentication to its services. Last month, notably, security researcher Cesar Cerrudo reported finding "a simple bypass trick for third-party applications to obtain access to a user's Twitter direct messages." Cerrudo said he made the discovery after finding that a Web application he was testing -- to which he hadn't granted authorization to access his direct messages -- was able to access and display those messages.
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