Valve's powerhouse PC gaming platform Steam suffered a significant security breach on Christmas day.
The company has confirmed that between 19:50 and 21:20 (UK time) on December 25th some users were able to see the personal details of other users' accounts. During the period, those who browsed pages containing personal information (such as the account or checkout page) had a chance of landing being presented with the same pages but linked to other profiles.
The problem affected only those who attempted to access said pages – which 34k people did during the said period.
The details that were potentially exposed include billing addresses, purchase histories, email addresses and the last few digits of Steam Guard phone numbers and credit card numbers. Valve assures users that not enough information would have been revealed to allow others to log into their accounts.
Valve is currently working with our web caching partner to identify users whose information was served to other users, and will be contacting those affected once they have been identified,” it explained. As no unauthorized actions were allowed on accounts beyond the viewing of cached page information, no additional action is required by users.”
How did it all happen, though?
Early Christmas morning (PST) the Steam Store was the target of a DoS attack which prevented the serving of store pages to users,” it added. Attacks against the Steam Store, and Steam in general, are a regular occurrence that Valve handles both directly and with the help of partner companies, and typically do not impact Steam users. During the Christmas attack, traffic to the Steam store increased 2000% over the average traffic during the Steam Sale.
In response to this specific attack, caching rules managed by a Steam web caching partner were deployed in order to both minimize the impact on Steam Store servers and continue to route legitimate user traffic. During the second wave of this attack, a second caching configuration was deployed that incorrectly cached web traffic for authenticated users. This configuration error resulted in some users seeing Steam Store responses which were generated for other users.
Incorrect Store responses varied from users seeing the front page of the Store displayed in the wrong language, to seeing the account page of another user.
Once this error was identified, the Steam Store was shut down and a new caching configuration was deployed. The Steam Store remained down until we had reviewed all caching configurations, and we received confirmation that the latest configurations had been deployed to all partner servers and that all cached data on edge servers had been purged.
We will continue to work with our web caching partner to identify affected users and to improve the process used to set caching rules going forward. We apologize to everyone whose personal information was exposed by this error, and for interruption of Steam Store service.”