Dropbox phishing attacks are relatively common and frequently fool employees into revealing their sensitive information or downloading malware.
Dropbox is a popular platform for sharing files and employees are used to receiving links advising them that files have been shared with them by their colleagues and contacts and phishers are taking advantage of familiarity with the platform.
There are two main types of Dropbox phishing attacks. One involves sending a link that asks users to verify their email address. Clicking the link directs them to a spoofed Dropbox website that closely resembles the official website. They are then asked to enter in their login credentials as part of the confirmation process.
Dropbox phishing attacks are also used to deliver malware such as banking Trojans and ransomware. A link is sent to users relating to a shared file. Instead of accessing a document, clicking the link will result in malware being downloaded.
Over the past few days, there has been a massive campaign using both of these attack methods involving millions of spam email messages. Last week, more than 23 million messages were sent in a single day.
Most of the emails were distributing Locky ransomware, with a smaller percentage used to spread Shade ransomware. There is no free decryptor available to unlock files encrypted by Locky and Shade ransomware. If files cannot be recovered from backups, victioms will have to dig deep.
Due to the rise in value of Bitcoin of late the cost of recovery is considerable. The malicious actors behind these attacks are demanding 0.5 Bitcoin per infected device – Around $2,400. For a business with multiple devices infected, recovery will cost tens if not hundreds of thousands of dollars.
According to F-Secure, the majority of malware-related spam messages detected recently – 90% – are being used to distribute Locky. Other security researchers have issued similar reports of a surge in Locky infections and spam email campaigns.
To prevent Locky ransomware attacks, businesses should install an advanced spam filtering solution to prevent malicious emails from being delivered to end users’ inboxes. Occasional emails are likely to make it past spam filtering defenses so it is important that all users receive security awareness training to help them identify malicious emails.
A web filter can be highly effective at blocking attempts to visit malicious websites where malware is downloaded, while up to date antivirus and anti-malware solutions can detect and quarantine malicious files before they are opened.
Backups should also be made of all data and systems and those backups should be stored on an air-gapped device. Ransomware variants such as Locky can delete Windows Shadow Volume Copies and if a backup device remains connected, it is probable that backup files will also be encrypted.
Best practices for backing up data involve three backup files being created, on two different media, with one copy stored offsite and offline. Backups should also be tested to make sure files can be recovered in the event of disaster.
The increase in ransomware attacks has prompted the National Institute of Standards and Technology (NIST) to develop new guidance (NIST SPECIAL PUBLICATION 1800-11) on recovering from ransomware attacks and other disasters. The draft guidance can be downloaded on this link.