Today I saw an interesting IMAP probe. These are usually background noise, occurring by the hundreds each day and mostly trying weak passwords against non-existent accounts. This particular login attempt was made on a valid alias, so I took a few seconds to dig deeper, and found an indicator of attack I hadn't seen before.
Immediately preceding the IMAP authentication attempt, the same IP address had issued one HTTP GET request and two HTTP POST requests for
/autodiscover/autodiscover.xml on the same domain (the file doesn't exist). Not being familiar with
autodiscover.xml, I looked up the documentation and it's a WPAD-like configuration discovery scheme for Outlook. Aside from people whose own Outlook clients and/or Exchange servers are spamming their own web server logs with requests, I couldn't find many people talking about seeing it in their httpd logs.
autodiscover.xml doesn't seem to be commonly scanned, spidered, or ab...