Threat actors use popular file-hosting or e-signature solutions as a disguise to manipulate their targets into revealing private information or downloading malware, according to Abnormal Security.
A file-sharing phishing attack is a unique type of phishing threat in which a cybercriminal poses as a known colleague or familiar file-hosting or e-signature solution and sends a target a malicious email containing a link to what appears to be a shared file or document.
Should the recipient click on the link, it initiates the second phase of the attack, which varies depending on the cybercriminal’s desired outcome—e.g., stealing login credentials or infecting the target’s device with malware.
File-sharing phishing attacks also make extensive use of social engineering. A primary component of these threats is leveraging the target’s familiarity with the impersonated party or service to lower their defenses.
File-sharing phishing attacks would be a pressing issue regardless of volume, as one single successful attack can have costly consequences.
File-sharing phishing attacks on the rise
Examining data collected between June 2023 and June 2024, Abnormal saw file-sharing phishing volume more than triple, increasing 350% over the year. The majority of these attacks were sophisticated in nature, with 60% exploiting legitimate domains, most commonly webmail accounts, such as Gmail, iCloud, and Outlook; productivity and collaboration platforms; file storage and sharing platforms like Dropbox; and e-signature solutions like Docusign.
“The trust that people place in these kinds of services—especially those with recognizable brand names—makes them the perfect vehicle for launching phishing attacks,” said Mike Britton, CISO at Abnormal Security. “Very few companies block URLs from these services because they aren’t inherently malicious. And by dispatching phishing emails directly from the services themselves, attackers hide in plain sight, making it harder for their targets to distinguish between legitimate and malicious communications. And when attackers layer in social engineering techniques, identifying these attacks becomes near-impossible.”
The finance industry was found to be most at risk, with file-sharing phishing attacks making up one in ten attacks. As financial institutions rely on file-sharing platforms to securely exchange documents, attackers have ample opportunities to slip in a fraudulent file-sharing notification among the sea of invoices, contracts, investment proposals, and regulatory updates.
The second most vulnerable industry was construction and engineering, followed by real estate and property management companies. These sectors not only rely heavily on frequent document transfers via file-sharing platforms, but also involve time-sensitive projects with large payouts. By exploiting the urgency of these exchanges, attackers have an opportunity to send file-sharing phishing attacks that appear time-critical and blend in seamlessly with legitimate emails.
BEC and VEC remain persistent threats
The biannual report also revealed the continued growth of business email compromise (BEC) and vendor email compromise (VEC) attacks:
BEC attacks grew by more than 50% over the last year, with attacks on smaller organizations jumping nearly 60% in the last half. 41% of Abnormal customers were targeted by VEC each week in the first half of 2024, a slight increase over the 37% targeted in the second half of 2023.
Construction and engineering firms, as well as retailers and consumer goods manufacturers, were most vulnerable to VEC attacks, with 70% of organizations receiving at least one VEC attack in the first half of the year.
Britton continued, “Cybercriminals are continuing to use email to target human behavior, and through a variety of techniques—whether it’s leveraging social engineering tactics for BEC, or using the guise of legitimate applications in their phishing schemes. The report findings underscore this deliberate shift away from overt payloads and threat signatures, and toward email attacks designed to manipulate behavior. Keeping up with these threats will require organizations to adapt accordingly, recentering their defenses on protecting humans as their most vulnerable endpoints.”