Avaddon Ransomware Still Using Excel 4.0 Macros

Ransomware criminals are still using malicious Excel 4.0 macros in campaigns. This week, Microsoft's security intelligence team noted that Avaddon was the latest malware to use the macros as an infection vector.

Avaddon is a form of ransomware that emerged in early June, and it is the latest malware campaign to use Excel 4.0 macros to spread in recent weeks. “The technique has been adopted by numerous campaigns, including ones that used COVID-19 themed lures,” it said. We documented this back in May when the NetSupport Manager RAT appeared.

“This week's campaign continues a recent trend of delivering ransomware as the immediate payload in email campaigns,” Microsoft said.

Avaddon searches for data to encrypt and then appends its own extension to encrypted files, dropping a ransom note in each folder that it affects. That links to a payment site accessible via the Tor network containing a unique ID that the victim can use to log in. They then see a ransom amount and instructions on how to pay.

The original ransomware campaign used in June used emails to distribute a JavaScript downloader that looked like an image file. However, online criminals will often change their techniques to keep victims guessing. Avaddon’s organizers reportedly posted to Russian-speaking hacker forums earlier this year, stating that they were operating an affiliate program for the ransomware. This would pay affiliates a portion of the ransom from any of their victims. One of those affiliates could well be responsible for the macro-based infection approach.

Macros are an old method of distributing malware that fell out of favor after Microsoft introduced more protections to stop them. Macros are disabled by default in more recent versions of Microsoft Office, meaning that criminals would have to persuade victims to turn them on. Enterprise IT admins can even set documents not to give users that option. However, not all of them do that, and many victims’ computers aren't managed by an admin at all. So this ancient delivery method is still a fruitful vector for attackers.

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