By Harsh Patel
The Cofense Phishing Defense Center (PDC) recently unearthed a new phishing campaign spoofing Skype, the popular video calling platform that has seen a recent spike in use amid the need to keep employees connected as they work remotely. This phishing attack was found in email environments protected by Proofpoint and Microsoft 365 EOP, landing in end-users’ inboxes.
With so many people working from home, remote work software like Skype, Slack, Zoom, and WebEx are starting to become popular themes of phishing lures. We recently uncovered an interesting Skype phishing email that an end user reported to the PDC.
Figures 1 and 2: Email Body
For this attack, the threat actor created an email that looks eerily similar to a legitimate pending notification coming from Skype. The threat actor tries to spoof a convincing Skype phone number and email address in the form of 67519-81987[@]skype.[REDACTED EMAIL]. While the sender address may appear legitimate at first glance, the real sender can be found in the return-path displayed as “sent from,” which also happens to be an external compromised account. Although there are many ways to exploit a compromised account, for this phishing campaign the threat actor chose to use it to send out even more phishing campaigns masquerading as a trusted colleague or friend.
It is not uncommon to receive emails about pending notifications for various services. The threat actor anticipates users will recognize this as just that, so they take action to view the notifications. Curiosity and the sense of urgency entice many users to click the “Review” button without recognizing the obvious signs of a phishing attack.
Upon clicking ‘Review’ users will be redirected via an app.link:
Finally, to the end phishing page:
The threat actor has chosen to utilize a .app top-level domain to host their attack. This TLD is backed by Google to help app developers securely share their apps. A benefit of this top-level domain is that it requires HTTPS to connect to it, adding security on both the user’s and developer’s end, which is great…but not in this case. The inclusion of HTTPS means the addition of a lock to the address bar, which most users have been trained to trust. Because this phishing site is being hosted via Google’s .app TLD it displays this trusted icon.
Figure 3: Phishing Page
Clicking the link in the email, the user is shown an impersonation of the Skype login page. If a well-trained user inspects the URL, they will see that the URL contains the word Skype (hxxps://skype-online0345[.]web[.]app). To add even further sense of authenticity, the threat actor adds the recipient’s company logo to the login box as well as a disclaimer at the bottom warning this page is for “authorized use” of that company’s users only. The username is auto-filled due to the URL containing the base64 of the target email address, thus adding simplicity to the phishing page and leaving little room for doubt. The only thing left for the user to do is to enter his or her password, which then falls into the hands of the threat actor.