module
Office 365 User Enumeration
| Disclosed |
|---|
| Sep 5, 2018 |
Disclosed
Sep 5, 2018
Description
Enumerate valid usernames (email addresses) from Office 365 using ActiveSync.
Differences in the HTTP Response code and HTTP Headers can be used to differentiate between:
- Valid Username (Response code 401)
- Valid Username and Password without 2FA (Response Code 200)
- Valid Username and Password with 2FA (Response Code 403)
- Invalid Username (Response code 404 with Header X-CasErrorCode: UserNotFound)
Note this behaviour appears to be limited to Office365, MS Exchange does not appear to be affected.
Microsoft Security Response Center stated on 2017-06-28 that this issue does not "meet the bar for security
servicing". As such it is not expected to be fixed any time soon.
Differences in the HTTP Response code and HTTP Headers can be used to differentiate between:
- Valid Username (Response code 401)
- Valid Username and Password without 2FA (Response Code 200)
- Valid Username and Password with 2FA (Response Code 403)
- Invalid Username (Response code 404 with Header X-CasErrorCode: UserNotFound)
Note this behaviour appears to be limited to Office365, MS Exchange does not appear to be affected.
Microsoft Security Response Center stated on 2017-06-28 that this issue does not "meet the bar for security
servicing". As such it is not expected to be fixed any time soon.
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