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By: Kian Mahdavi, Cofense Phishing Defense Center

The Cofense Phishing Defense Center (PDC) is seeing continued growth in phishing attacks which harvests users’ credentials via genuine file-sharing websites, which are found in environments protected by Proofpoint’s Secure Email Gateway (SEG). A huge factor in this campaign is the confidence users have in emails containing the “trusted” Dropbox reference.

It is tricky for SEGs to keep up with attempts to spread phishing attacks and malware via sharing services such as Dropbox, ShareFile, WeTransfer, Google Docs, Egnyte and even SharePoint. Fortunately, a few of our clients’ users reported the phishing emails via the Cofense Reporter button.

The “traditional” methodology for attackers was to “break in.” Nowadays, they easily can “login,” thanks to sharing sites.

Figure 1 – Body of email showcasing the victory of this attack tying in with user interaction

The spear phishing attack sends a link requesting users to access a purchase order form with a (.pdf) extension. Upon clicking, the attack automatically redirects the user to their default web browser, requesting to click the “Download” button. The website will begin the download inside the “Downloads” folder. Nothing sinister going on, right?

The ‘sent addresses’ TLD – “actionsportsequipment[.]com” – coincidentally relates to the nature of the client’s industry; this demonstrates the extent the attackers went to, in a bid to slip through the “secure” environment. One must question themself: “Was I expecting this transfer?” and “Am I expecting to receive a purchase order from this sender?”

Moreover, since the emails have been authenticated against Dropbox’s internal servers, the emails pass basic email security checks such as DKIM and SPF.

Figure 2 & 3 – Downloadable purchase order file

Once the download has been completed, the user is prompted to open the (.html) link assuming the “purchase order” form would appear, however upon clicking, the campaign redirects the user to a supposed “Microsoft” login page.

In this case, the attackers used the free website builder “Weebly.com” … yet another legitimate source, further deceiving the security measures in place with trusted redirect domains and IPs which will naturally continue to be white-listed and deemed “safe” since millions of users share data with one another on a daily basis.

For this reason, the presence of the padlock appears, adding not only security on both parties, but also the illusion that the website is “secure.”

Figure 5 – Phishing site built by Weebly

Once credentials have been supplied, the campaign redirects the user to the authentic ‘office[.]com’ webpage, which could even be enough to assure users it was a genuine procedure. A user’s personal data could potentially be in the hands of the threat actor, assuming they logged in with their true Microsoft credentials.

Figure 6 – Redirect to Microsoft Office webpage  

Indicators of Compromise:

Network IOC IP
hXXps://www[.]dropbox[.]com/l/AADOPQGXtuDK03QYuvJqI0MbDlDxBTV28Cs
hXXps://www[.]dropbox[.]com/l/AAAtWq-LVZcqXBnFLinUi9rB3LpEijuPo78
162[.]125[.]6[.]1
hXXps://helpsupport0ffice20[.]weebly[.]com/ 199[.]34[.]228[.]53
199[.]34[.]228[.]54

LEARN MORE about the Cofense Phishing Defense Center. See how the PDC’s managed phishing response and remediation stops the phishing attacks that elude email gateways.

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