The Steam video game service recently faced connectivity issues after a huge increase in bandwidth and apparent DoS attack on Christmas Day

Valve issued a statement of apology yesterday regarding what is now being called a “configuration error” that occurred on Christmas. The error exposed allowed tens of thousands of users to view the account information belonging to someone else instead of their own when accessing their account.

The holiday season often marks a time of connectivity and patching issues as an untold multitude of new gamers take to the internet just after Christmas to try out their new consoles and games. Every year, online gaming services like Steam come under huge amounts of bandwidth usage, and sites often crash or temporarily go offline while servers reboot.

This year was marked by especially trying problems for Steam. The error in viewing another person’s account information, the Steam Store homepage was often displaying in a language other than what it should. The two errors seemed to be related, and the service went offline intermittently Christmas day.

According to the statement by Valve, Steam was the target of a DoS attack early Dec. 25. In addition to being attacked by hackers, Steam was experiencing a reported 2000 percent increase in traffic due to the holiday Steam Sale. The combination of these two events caused caching issues which resulted in users seeing account information, libraries, and Steam Store responses belonging to other users. Compromised data included billing addresses, the last four digits of Steam Guard phone numbers, purchase history, the last two digits of credit card information and email addresses.

The entire statement released by Valve:

What happened

On December 25th, a configuration error resulted in some users seeing Steam Store pages generated for other users. Between 11:50 PST and 13:20 PST store page requests for about 34k users, which contained sensitive personal information, may have been returned and seen by other users.

The content of these requests varied by page, but some pages included a Steam user’s billing address, the last four digits of their Steam Guard phone number, their purchase history, the last two digits of their credit card number, and/or their email address. These cached requests did not include full credit card numbers, user passwords, or enough data to allow logging in as or completing a transaction as another user.

If you did not browse a Steam Store page with your personal information (such as your account page or a checkout page) in this time frame, that information could not have been shown to another user.

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. As no unauthorized actions were allowed on accounts beyond the viewing of cached page information, no additional action is required by users.

How it happened

Early Christmas morning (Pacific Standard Time), the Steam Store was the target of a DoS attack which prevented the serving of store pages to users. 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.

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