Phishing in a Bucket: Utilizing Google Firebase Storage

Credential phishing is a real threat that's targeting organizations globally. Threat actors are finding smart and innovative ways to lure victims to covertly harvest their corporate credentials. Threat actors then use these credentials to get a foothold into an organization to further their malicious agendas.

We recently observed a series of unique phishing campaigns targeting our global customers. While these campaigns used common phishing lures, what made them unique was the adoption of Google firebase storage URLs embedded in the phishing messages. In effect, actors leverage the repute and services of Google Cloud’s infrastructure to host their phishing credential harvesting pages.

Google Firebase is a mobile and web application development platform. Firebase Storage is backed by Google Cloud Storage and provides secure file uploads and downloads for Firebase apps. Using the firebase storage API one can store data in a Google Cloud Storage bucket which is a storage solution with high availability and global redundancy.

This phishing campaign although low in volume seems to be targeting a range of industries, as well as being detected by our spam traps. Some exemplar phishing messages used in this campaign are illustrated here. The major themes include payment invoice, upgrade email account, release pending messages, verify account, account error, change password, etc.

Figure 1: Scammers using the Covid-19 pandemic and internet banking as an excuse to lure the victims into clicking on the fake vendor payment form that leads to the phishing page hosted on Firebase Storage.

Figure 2: Fake Microsoft outlook mailbox upgrade phishing lure email containing link to phishing page hosted on firebase storage.

While the phishing messages seem quite convincing, some subtle imperfections exist such as variation in font and poor graphics, etc.

Figure 3: Fake Email account deactivation phishing email sent to victims to trick them to click on the link that takes them to an office 365 phishing page hosted on Firebase Cloud Storage.

Figure 4: Fake Microsoft office 365 phishing lure tricking the user to review pending emails. Clicking on the link takes the victim to the office 365 phishing page hosted on Firebase Storage.

Figure 5: Fake Microsoft phishing message sent to victims to lure them to click on the review button to review and release quarantined messages held by email server. Clicking on the link takes the victim to the phishing page hosted on Firebase Storage bucket.

Figure 6: Fake office 365 Phishing message asking victim to release messages held by mail server. Clicking on the link takes the victim to an office 365 credential phishing page hosted on firebase storage.

In subsequent iterations we observed the phishing scope expand from fake Microsoft Office 365 emails to fake bank emails as illustrated here.

Figure 7: Fake Bank of America Phishing email. Clicking on the link takes the victim to an office 365 credential phishing page hosted on firebase storage.

The final credential phishing landing pages hosted on the Google cloud storage platform and accessed via the firebase storage URLs are illustrated here. Most of these pages are variants of the Microsoft Outlook and Office 365 phishing pages, mainly designed to harvest corporate credentials.

Figure 9: Fake Microsoft Outlook account setting credential phishing page hosted on Google cloud storage accessed via firebase storage URLs.

Figure 11: Fake Bank of America phishing page, hosted on google storage to collect victim’s information.

Conclusion

Phishing is a real threat targeting corporates and individuals alike. Cybercriminals are constantly evolving their techniques and tools to covertly deliver their messages to unwitting victims. Credentials harvested as a result of phishing are often used as an initial trigger for launching various types of advanced attacks. In this campaign, threat actors leverage the reputation and service of the Google Cloud infrastructure to conduct phishing by embedding Google firebase storage URLs in phishing emails. This campaign is yet another example of the bad guys using cloud infrastructure to host their phishing pages.

Trustwave Secure Email Gateway (SEG) detects these phishing messages. We advise all users to be careful before clicking on any URLs and check their browser’s address bar before submitting credentials to any login form.

IOCs:

• hxxps://firebasestorage[.]googleapis[.]com/v0/b/quartry943499943442.appspot.com/o/index.html?alt=media&token=f9fac252-84eb-4a37-b20c-eba25a81ccd1#victim@victim.com
• hxxps://firebasestorage[.]googleapis[.]com/v0/b/selvet20202.appspot.com/o/inde.html?alt=media&token=693c1f1d-003d-4930-842a-d9eaad266376
• hxxps://firebasestorage[.]googleapis[.]com/v0/b/upgradeaccoun.appspot.com/o/roundcube%2Fcn%2Findex2ajax.html?alt=media&token=4440a1ce-711c-4735-9261-2c3239b975e5&email=victim@victim.com
• hxxps://firebasestorage[.]googleapis[.]com/v0/b/greatwebmails.appspot.com/o/mndaass%2Findex.html?alt=media&token=1c5e6903-1a39-45a8-a269-e1f7f8ae5a58# victim@victim.com
• hxxps://firebasestorage[.]googleapis[.]com/v0/b/auth20-outlook.appspot.com/o/ind.htm?alt=3Dmedia&token=3D0f1a994b-271e-4be8-be2d-c30401587782#victim@victim.com
• hxxps://firebasestorage[.]googleapis[.]com/v0/b/office-8d703.appspot.com/o/ind.htm?alt=3Dmedia&token=3Dbbcdd20c-bc6e-46fe-ac1b-5c7c8cdd0123#victim@victim.com
• hxxps://firebasestorage[.]googleapis[.]com/v0/b/webmail-a660b.appspot.com/o/indexobf.html?alt=media&token=b21c31dd-25f6-45bb-89dd-397bc695b65f