Microsoft Patches Hotmail Password Bypass Flaw

Microsoft has patched a recently disclosed password reset vulnerability in Hotmail, which exposed a user base of some 360 million people to having their accounts compromised. Unfortunately, says Vulnerability Laboratory, the firm that discovered the flaw initially, the patch might not have arrived soon enough.

The flaw was discovered on April 6. A Vulnerability Laboratory senior researcher, Benjamin Kunz Mejri, identified the problem around the same time that a hacker from Saudi Arabia did. The Saudi hacker’s discovery was leaked to various forums, and from there it spread. Within days, offers to crack any Hotmail account within minutes, for as little as $20 appeared on forums across the Web.

“Remote attackers can bypass the password recovery service to setup a new password and bypass in place protections (token based). The token protection only checks if a value is empty then blocks or closes the web session,” the Vulnerability Labs disclosure explains.

Thus, an attacker could simply use random values, such as “+++)-,” in order to bypass the token protection.

The vulnerability was used to compromise various Hotmail accounts, including those with unique addresses, such as ‘xxx’ or two character usernames. In addition, social networking profiles tied to the compromised Hotmail account were exposed, as well as PayPal and Liberty Reserve accounts.

While eventually patched, the flaw was open for 14 days. Microsoft has not commented on the issue. More information can be found here and here.