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14.01.2019 13:18

COOL: Hackers Using Zero-Width Spaces to Bypass MS Office 365 Protection

Swati Yoav Nathaniel is writing about a new way to evade URL-detaction with the Office365.


His idea is to put Zero-Width statements into the URL to trick the MS ATP-detection algorythm.

So, it's about to enhance our own detection filters with the below list to stay on top of detections.

  • ​ (Zero-Width Space)
  • ‌ (Zero-Width Non-Joiner)
  • ‍ (Zero-Width Joiner)
  •  (Zero-Width No-Break Space)
  • 0 (Full-Width Digit Zero)

His poc was.

In a Z-WASP phishing attack, the Zero-Width Non-Joiner (‌) is added to the middle of a malicious URL within the RAW HTML of an email.

Microsoft email processing did not recognize this URL as a legitimate URL, and neither applied URL reputation checking nor converted it with Safe Links for post-click checking. The email was delivered to the intended recipient; but in their inbox, users did not see the ZWSPs in the URL.

When the end-users clicked on the link in the email, they were taken to a credential harvesting phishing site. In the example below, Chase Bank was spoofed.