A new phishing campaign has been identified that uses the novel tactic of attaching corrupted Microsoft Word files to emails. The files themselves do not contain any malicious code, so scans of the attachments by email security solutions may not flag the emails as malicious.
In order to get the recipient to open the email, the threat actor impersonates the HR department or payroll team, as employees will typically open these messages. The attached files have file names related to payments, annual benefits, and bonuses, which employees may open without performing standard checks of the email, such as identifying the true sender of the message. Many employees place a moderate amount of trust in Word files, as if they contain a macro, it should not run automatically if the Word document is opened.
The threat actor relies on the employee’s curiosity to open the file and the way that operating systems handle corrupted files. The file recovery feature of Microsoft Word will attempt to recover corrupted files. The user will be informed that parts of the file contain unreadable content, and the user is prompted to confirm if they would like the file to be recovered. The documents have been crafted to ensure that they can be recovered by Word, and the recovery will present the user with a QR code that they are told they must scan to retrieve the document.
The document includes the logo of the company being targeted, and the user does not need to “enable editing” to view the contents of the document, so they may mistakenly believe they are safe. If they scan the QR code using their mobile device, they will be directed to a phishing page where they are asked to enter their Microsoft credentials on a phishing page that is an exact match of the genuine Microsoft login prompt.
Businesses with spam filter software may not be protected as email security solutions often fail to scan corrupted files. For instance, the phishing emails bypass Outlook spam filters according to the researchers at Any.Run who identified the campaign. That means the emails may be delivered to inboxes, especially as the messages do not contain any content in the body of the email indicative of a phishing attempt.
If the user opens the file and scans the QR code, they will switch from their desktop or laptop to their mobile phone. Mobile devices rarely have the same level of security protection, so corporate anti-phishing controls such as web filters will likely be bypassed.
Threat actors are constantly developing new ways to trick employees in their phishing campaigns, which is why it is important to run security awareness training programs continuously, updating the training content with new training material in response to threat actors’ changing tactics. By warning employees about this method, they should recognize the scam for what it is if they receive an email with a corrupted file attachment. That is easy to do with a security awareness training platform such as SafeTitan. New training content can be quickly created and rolled out to all users as part of their monthly allocation of training modules. It is also easy to add this type of threat to the SafeTitan phishing simulator to test how employees respond to this new threat type.
As the researchers demonstrated, Microsoft fails to detect the threat, demonstrating why it is important to bolster your M365 phishing defenses with a third-party solution, such as PhishTitan from TitanHQ. PhishTitan integrates seamlessly with Microsoft 365 to augment protection and catches the phishing threats that Microsoft misses. PhishTitan will also add a banner to all inbound emails that come from external sources, giving users a clear flag that these emails are not genuine. The HR department and payroll have internal email addresses.
An email security solution with email sandboxing is also advisable for deep inspection of file attachments, including the ability to read QR codes. Spam filters for incoming mail should also have machine learning and AI-based detection capabilities for identifying emails that deviate from the messages typically received by the business.
All of these features are part of TitanHQ’s email security suite. Give the team a call today to find out more.