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Attacking Exchange With MailSniper

posted Oct 7, 2016, 9:15 AM by Beau Bullock

I’ve added in a few modules to MailSniper that will assist in remote attacks against organizations that are hosting an externally facing Exchange server (OWA or EWS). Specifically, the modules are Get-GlobalAddressList, Invoke-PasswordSprayOWA, and Invoke-PasswordSprayEWS.

Very often on external penetration tests we perform a reconnaissance phase that might yield us some email addresses or usernames of an organization. If we can successfully find valid credentials for any one of them, and the organization has an Outlook Web Access or Exchange Web Services portal it is possible to download the entire Global Address List from the Exchange server. So, from one valid credential we can now have access to all email addresses for every employee of an organization.

Additionally, I wrote in two modules for password spraying Outlook Web Access and Exchange Web Services to MailSniper. Password spraying is an attack where instead of trying to brute force many password attempts for a single user account we try one password across many user accounts. This helps avoid account lockout and will still result in us obtaining valid credentials as users still pick passwords like “Fall2016”. Both of the functions are multi-threaded. Just pass the -Threads option and specify a number of threads (15 seems to be a pretty good starting point).

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