The file hosting service Dropbox is being abused in a novel phishing campaign that exploits trust in the platform to harvest Microsoft 365 credentials. The campaign targeted 16 employees of an organization who received an email from the no-reply[@] account, a legitimate email account that is used by Dropbox. The emails included a link that directed the recipients to a Dropbox-hosted PDF file, which was named to appear as if it had been created by one of the organization’s partners. If the PDF file was opened, the user would see a link that directs them to an unrelated domain – mmv-security[.]top. One of the employees was then sent a follow-up email reminding them to open the PDF file that was sent in the first email. They did, and they were directed to a phishing page that spoofed the Microsoft 365 login page. A couple of days later, suspicious logins were detected in the user’s Microsoft 365 account from unknown IP addresses, which were investigated and found to be associated with ExpressVPN, indicating the attacker was using the VPN to access the account and mask their IP address.

Multifactor authentication was correctly configured on the account but this appears to have been bypassed, with the logins appearing to use a valid MFA token. After capturing credentials, the employee is thought to have unknowingly approved the MFA authentication request which allowed the account to be compromised. The attacker gained access to the user’s email account and set up a new rule that moved emails from the organization’s accounts team to the Conversation History folder to hide the malicious use of the mailbox. Emails were also sent from the account to the accounts team in an apparent attempt to compromise their accounts.

Phishing attacks are becoming increasingly sophisticated and much more difficult for end users to identify. Security awareness training programs often teach users about the red flags in emails they should look out for, such as unsolicited emails from unknown senders, links to unusual domains, and to be wary of any requests that have urgency and carry a threat should no action be taken. Impersonation is common in phishing attacks, but in this case, the impersonation went further with the emails sent from a valid and trusted account. That means that the email is more likely to be trusted and unlikely to be blocked by email security solutions, especially as the emails include a link to a file hosted on a trusted platform. This was also a staged attack, with follow-up emails sent, which in this case proved effective even though the second email was delivered to the junk email folder. The login page to which the user was directed looked exactly the same as the genuine login prompt for Microsoft 365, aside from the domain on which it was hosted.

Many businesses have configured multifactor authentication on their Microsoft 365 accounts, but as this attack demonstrates, MFA can be bypassed. The sophisticated nature of phishing attacks such as this demonstrates how important it is for businesses to have advanced defenses against phishing. TitanHQ’s anti-phishing solutions use AI and a large language model (LLM) with proprietary threat intelligence currently not found in any other anti-phishing and anti-spam software solutions on the market. All emails are scanned – internal and external – for phrases and keywords that are unusual and could indicate malicious intent. All URLs are checked against various threat intelligence feeds to identify malicious URLs, and URLs are rewritten to show their true destination. The solution also learns from feedback provided by users and detection improves further over time. The curated and unique email threat intelligence data is unmatched in visibility, coverage, and accuracy, and TitanHQ’s anti-spam and email security solutions feature sandboxing, where attachments are subjected to deep analysis in addition to signature-based anti-virus scanning. When a malicious email is detected, all other instances are removed from the entire M365 tenant.

If you want to improve your defenses against sophisticated phishing attacks give the TitanHQ team a call. If you are a Managed Service Provider looking for an easy-to-use solution to protect your clients from phishing and malware, look no further than TitanHQ. All solutions have been developed from the ground up to meet the needs of MSPs to better protect their customers from spam, phishing, malware, and BEC attacks.