Microsoft Exchange Autodiscover bugs leak 100K Windows credentials

Bugs in the implementation of Microsoft Exchange’s Autodiscover feature have leaked approximately 100,000 login names and passwords for Windows domains worldwide.

In a new report by Amit Serper, Guardicore’s AVP of Security Research, the researcher reveals how the incorrect implementation of the Autodiscover protocol, rather than a bug in Microsoft Exchange, is causing Windows credentials to be sent to third-party untrusted websites.

Microsoft Exchange uses an Autodiscover feature to automatically configure a user’s mail client, such as Microsoft Outlook, with their organization’s predefined mail settings.

When an Exchange user enters their email address and password into an email client, such as Microsoft Outlook, the mail client then attempts to authenticate to various Exchange Autodiscover URLs.

To test this, Guardicore registered the following domains and set up web servers on each to see how many credentials would be leaked by the Microsoft Exchange Autodiscover feature.

Serper has provided a few suggestions that organizations and developers can use to mitigate these Microsoft Exchange Autodiscover leaks.

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