Phishing Attackers Are Abusing WeTransfer to Evade Email Gateways

By Jake Longden

The Cofense Phishing Defense Center has observed a wave of phishing attacks that utilize the legitimate file hosting site WeTransfer to deliver malicious URLs to bypass email gateways. The attacks span major industries like banking, power, and media. Here’s how they work.

Email Body:

The email body is a genuine notification from WeTransfer which informs the victim that a file has been shared with them. The attackers utilise what appears to be compromised email accounts to send a genuine link to a WeTransfer hosted file. As these are legitimate links from WeTransfer, this allows them to travel straight through security checks at the gateway.

WeTransfer allows for the addition of a note to the email to clarify why the file was sent. Here, the threat actor will often write a note stating that the file is an invoice to be reviewed. This is a commonly observed phishing technique to pique the user’s interest.

Fig 1. Email body

Phishing Page:

When the user clicks on the “Get your files” button in the message body, the user is redirected to the WeTransfer download page where a HTM or HTML file is hosted and thus downloaded by the unsuspecting victim. When the user opens the .html file, he or she is redirected to the main phishing page.

Fig 2. WeTransfer Hosted file

In the final stage of the attack, victims are asked to enter their Office365 credentials to login. More often than not, we see a Microsoft Service being targeted, however we have observed other targeted brands.

Fig 3. Phishing Page

Gateway Evasion

As WeTransfer is a well-known and trusted file hosting system, used to share files too large to attach to an email, these links will typically bypass gateways as benign emails, unless settings are modified to restrict access to such file sharing sites. The PDC has observed this attack method to bypass multiple gateways. These include ProofPoint, Office365 Safe Links,  and Symantec.

Useful Resources for Customers

Description
Triage Yara rule: PM_WeTransfer_File_Download
PhishMe Templates: “File Transfer”
Cofense Intelligence: https://www.threathq.com/p42/search/default#m=26412&type=renderThreat 


Other Ways Cofense Can Help

The Cofense Phishing Defense Center identifies active phishing attacks in enterprise environments. Learn how our dedicated experts provide actionable intelligence to stop phishing threats.

75% of threats reported to the Cofense Phishing Defense Center are credential phish. Protect the keys to your kingdom—condition end users to be resilient to credential harvesting attacks with Cofense PhishMeTM.  Our solution offers a phishing simulation to protect against file-transfer attacks like the one described in this blog.

According to the Cofense Phishing Defense Center, over 91% of the credential harvesting attacks they identify bypassed email gateways. Remove the blind spot—get visibility of attacks with Cofense ReporterTM.

Quickly turn user reported emails into actionable intelligence with Cofense TriageTM. Reduce exposure time by rapidly quarantining threats with Cofense VisionTM.

Attackers do their research. Every SaaS platform you use is an opportunity for attackers to exploit it. Understand what SaaS applications are configured for your domains—do YOUR research with Cofense CloudSeeker.

Thanks to our unique perspective, no one knows more about current REAL phishing threats than Cofense. To raise your understand, read the 2019 Phishing Threat & Malware Review.

 

All third-party trademarks referenced by Cofense whether in logo form, name form or product form, or otherwise, remain the property of their respective holders, and use of these trademarks in no way indicates any relationship between Cofense and the holders of the trademarks.

This ‘Voice Mail’ Is a Phish—and an Email Gateway Fail

By Milo Salvia and Kamlesh Patel

The Cofense Phishing Defense CenterTM has observed a phishing campaign that masquerades as a voicemail message from a well-known company. The goal is to steal your domain credentials by mimicking the Outlook Web App (OWA). 

Email Body: 

The message body is designed to mimic your typical VOIP missed call message delivered via email when a user misses a call. A simple HTML box appears with a blue hyperlink, Play Voice. One would assume it was meant to say Play Message or Play Voice Message. This could indicate that English is not the threat actor’s first language and the original message was mistranslated. It’s the first indicator that something is not quite right about this message. 

Fig 1. Email Body

Message body in HTML:  

If you look at the message body in HTML, you can see that the embedded hyperlink redirects to www[.]lkjhyb[.]com_dg[.]php=”. As you can tell, the URL has been wrapped by a URL filtering service. 

 

<Div align=”center” style=”text-align: center;”> 

<a href=”hxxps://urldefense[.]proofpoint[.]com/v2/url?u=hxxps-3A__www[.]lkjhyb[.]com_dg[.]php=“>Play Voice</a></div> 

</span></font></div>* 

 

Fig 2. Email Body in Plain Text  

Email Headers: 

A closer look at the header information reveals that the threat originates from the domain “protogonay.com. Further research into this domain suggests that it could be a throwaway domain—no company or website can be found that is directly linked to the name 

ext-caller108[@]progonay[.]com.” The threat source itself uses ext-caller108 to add legitimacy to the voicemail ruse. 

** From: Voice Ext <ext-caller108[@]progonay[.]com> 

To: <dxxx.mxxx@axxxx.com> 

Subject: Voice call from ******* (39 seconds) 

Date: Wed, 22 May 2019 08:23:33 -0700 

Message-ID: <20190522082333.8F2288151F642334@progonay.com> 

Content-Type: text/html; charset=”iso-8859-1″ 

X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-05-22_08:,, 

 signatures=0 

X-Proofpoint-Spam-Details: rule=notspam policy=default score=1 priorityscore=1501 malwarescore=0 

 suspectscore=2 phishscore=0 bulkscore=0 spamscore=1 clxscore=-94 

 lowpriorityscore=0 mlxscore=1 impostorscore=0 mlxlogscore=206 adultscore=0 

Fig 3. Email Headers

Phishing Page:  

Once the user clicks on the “Play Voice (sic)” hyperlink, it redirects to what looks like the default corporate Outlook Web App (OWA) login page. This page is designed to steal your O365 domain credentials. As we can see, it asks the victim to supply domain/username:  and password.  

Fig 4. Phishing Page 

Gateway Present:  

This threat was found in an environment running Proofpoint Email Gateway and URL filter. 

Conclusion:  

Threat actors pull out the stops to deliver malicious messages to users’ inboxes. This “voice mail” message is yet another creative example.  

To help protect against this type of credential phish, Cofense PhishMeTM offers a template called “Play Voice Message.” 

Learn more about evolving phishing tactics and techniques—view the Cofense Phishing Threat and Malware Review 2019. 

 

All third-party trademarks referenced by Cofense whether in logo form, name form or product form, or otherwise, remain the property of their respective holders, and use of these trademarks in no way indicates any relationship between Cofense and the holders of the trademarks.