Hack to the Future: The Return of Macro Malware

Threats & Hacks

We who write stuff in the security industry are used to dashing off sentences like, “Online attacks are becoming more and more advanced” or “Malware is continually evolving in sophistication.”

But in the past year we experienced a surprising throwback to one type of malware from an earlier era. Malware that uses a rather old technique, but it’s causing plenty of trouble nonetheless. It kinda feels like we’ve gone back in time.

I’m talking about macro malware. It’s something we hadn’t seen prominently since the early 2000’s. And now, as touched on in our just released Threat Report covering the 2015 threat landscape, it has reared its head again.

What is macro malware?

Macro malware takes advantage of the macro feature in Office documents to execute commands. And macros are simply shortcuts the user can create for repeated tasks.

For example, let’s say you are creating a document in Word and you find yourself repeatedly editing text to be red with a yellow highlight, 16 point, italic and right aligned. To save time, you can create a macro of your commands and then whenever you need that kind of style, simply run the macro.

A little history

Macro malware was common back in the 1990’s and early 2000’s. The first macro malware, Concept, was discovered in 1995, although it was basically harmless, simply displaying a dialogue box. In 1999, one of the most notorious macro malware, Melissa, was discovered. Melissa emailed itself to 50 addresses in the user’s address book, spreading to 20% of the world’s computers.

But macro malware wouldn’t last long. When Microsoft released Word 2003, the default security settings were changed to stop macros from automatically running when a document opened. This made it more difficult to infect a computer through macros and attackers mostly dropped them to focus on other methods.

So what happened? Why is it back again?

The re-emergence, according to Sean Sullivan, Security Advisor in F-Secure Labs, may be correlated with the decline of exploitable vulnerabilities due to security improvements in today’s common software applications like Microsoft Office. Exploits have been one of the most common ways to infect machines in recent years, but with fewer software holes to exploit, malware authors seem to be reverting to other tricks.

How it’s successful

Today’s macro malware attempts to get around Microsoft’s default settings with a simple trick. When a document is opened, the information inside doesn’t appear properly to the viewer – for example, sometimes the document looks like scrambled gobbledygook. Text in the document claims that macros, or content, must be enabled for proper viewing.

Here’s one example:

example of macro malware

Curiosity? Just plain unaware? Whatever the reason, as Sean says, the malware’s reappearance has been successful because “People click.”

Once macros have been enabled, the malicious macro code is executed – which then downloads the payload.

Macro malware is used by crypto-ransomware families like Cryptowall and the newest threat Locky. These families encrypt the data on a computer and then demand payment to unencrypt it. Although we don’t know for sure, it’s possible it was macro malware that was used in the holding of a Hollywood hospital for ransom last month.

The banking Trojan Dridex, which allows attackers to steal banking credentials and other personal info from infected machines, also uses the technique.

How to avoid it

Fortunately, if you use security from F-Secure, you’re protected from these threats. But aside from that, the old advice still holds: Be wary of email attachments from senders you don’t know. And take care not to enable macros on documents you’ve received from sources you’re not 100% sure of.

 

“Back to the Future” banner image courtesy of Garry Knight, flickr.com

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