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Security advisories | Aug 22, 2019

Office 365 Phishing Follow-Up

The Threat

The eSentire Threat Intelligence team continues to observe various Microsoft themed phishing emails leveraging cloud services to host Office 365 credential phishing pages [1].

Due to the convincing nature of these phishing emails, end-users are encouraged to increase their awareness of this threat. Network administrators are encouraged to review the recommendations below and ensure email controls are effective.

What we're doing about it

  • Identified phishing pages have been reported to Microsoft
  • The Threat Intelligence team is monitoring this threat for additional information

What you should do about it

Users

  • Review below images of recent phishing emails for examples of what to expect
  • Review emails for suspicious indicators (such as unknown sender/ suspicious URLs) prior to opening links or attachments
  • Be cautious of generic Office 365 login pages lacking branding for your organization

Network/Email Administrators

eSentire has observed consistent use of blob[.]core[.]windows[.]net or azurewebsites[.]net to host phishing links, and recommends the following:

  • Consult your email security provider to ensure phishing emails using the above links are sufficiently blocked
  • Alternatively, implement Exchange rules to redirect emails containing the links to a monitored inbox (see Figure 5 for an example). This will effectively prevent the email from reaching the intended target, while allowing any legitimate emails to still be reviewed and forwarded. In our testing, eSentire has not caught any legitimate email using this method.

If these domains are used legitimately and cannot be blocked, ensure staff are aware of the risk and verify sender addresses before opening links or attachments

Additional information

Emails observed over the last month have generally been Microsoft themed. When combined with the use of Microsoft links, the authenticity of the email can be difficult to ascertain.

Observed lures in this campaign include fake PowerPoint presentations (Figure 1), Office 365 forwarding alerts (Figure 2), Office 365 email quarantine (Figure 3), and Microsoft Excel pages (Figure 4).

Appendix:

Figure 1: PowerPoint lure, clicking open or “Roadmap for Q4’19” leads to a blob[.]core[.]windows[.]net Office 365 phishing page.

[image src="/assets/f1b2d16511/fig1.png" id="2390" width="404" height="330" class="leftAlone ss-htmleditorfield-file image" title="fig1"]

Figure 2: Forwarding/redirect rule lure. If “Investigate” is clicked, the users is directed to a blob[.]core[.]windows[.]net Office 365 phishing page.

[image src="/assets/fe58b08860/fig2-v2.png" id="2391" width="482" height="263" class="leftAlone ss-htmleditorfield-file image" title="fig2 v2"]

Figure 3: Office 365 email quarantine lure. If “Review Here” is clicked, the user is directed to a blob[.]core[.]windows[.]net Office 365 phishing page.

[image src="/assets/158c0b2b77/fig3.png" id="2392" width="531" height="345" class="leftAlone ss-htmleditorfield-file image" title="fig3"]

Figure 4: Microsoft Excel Lure. When the user clicks on either “To Open” or “Bonus 2010 form.xls” they are redirected to a credential phishing page hosted on blob[.]core[.]windows[.]net.

[image src="/assets/ca8f8a3c16/fig4.png" id="2393" width="562" height="308" class="leftAlone ss-htmleditorfield-file image" title="fig4"]

Figure 5: Transport Rule example

[image src="/assets/14612aae21/fig5.png" id="2394" width="551" height="608" class="leftAlone ss-htmleditorfield-file image" title="fig5"]

References:

[1] https://www.esentire.com/security-advisories/hex-encoded-links-point-to-phishing-pages-on-microsoft-cloud-services/