Why Microsoft's New Office 2016 Macro Control Feature Matters

Macro attacks on Windows machines have been on a tear over the past year. This 1990s-era threat’s comeback has been spotted in both targeted and more widespread attack campaigns.

Microsoft says some 98% of all Office threats employ malicious macros, and recent events illustrate the phenomenon: high-profile attack campaigns including the most recent point-of-sale (PoS) attacks on some 100 organizations in the hospitality, restaurant, and retail industries, use malicious macros, and Neutrino--also known as Kasidet—surged in February, using malicious Microsoft Office macros to spread the backdoor malware that also drops Dridex banking malware on its victims’ machines. Ransomware attacks often arrive via attachments with Word macro downloaders.

Even the infamous blackout attack in the Ukraine used a malicious macro. “A two-year old Office [vulnerability and a] macro was enabled in [their] Office suites," says Cameron Camp, a security researcher at ESET.

The good news is that Microsoft has added a new feature to Office 2016—currently in RTM release--that lets organizations designate macro use to specific situations and to block macro enablement in high-risk situations. Microsoft long ago removed the by-default enablement of macros, but users can enable macros if they need them for automating tasks such as automatically opening Word files, filling in forms, or performing calculations. With attackers upping their social engineering game in spear phishing emails, macros have become one of the most popular attack vectors in the past year, prompting calls for more controls over macro code.

“Macro-based malware is on the rise and we understand it is a frustrating experience for everyone. To help counter this threat, we are releasing a new feature in Office 2016 that blocks macros from loading in certain high-risk scenarios,” the Microsoft Malware Protection Center said in a late March blog post announcing the new feature. “This feature can be controlled via Group Policy and configured per application. It enables enterprise administrators to block macros from running in Word, Excel and PowerPoint documents that come from the Internet.”

Among these risky scenarios: documents downloaded from the Internet; document attachments that were sent from outside the organization; and documents opened from file-sharing or other public shares.

Microsoft isn’t the only vendor seeing macro attacks surge. Intel’s McAfee Labs recently reported a massive spike in macro malware over the past 18 months. Year over year growth in macro threats tripled by the end of the third quarter of 2015, with 45,000 cases of new macro malware during that quarter, up from under 10,000 in the third quarter of 2014. According to McAfee, macro malware was at their highest level since 2009.

But today’s macro attacks are more sophisticated than those of the ‘90s: they’re often encrypted or obfuscated by attackers, thus making them more difficult to detect.

The use of malicious macros in the December cyberattack on Western Ukraine’s power supply demonstrated how macros can be part of the attack chain in a destructive cyberattack. The attackers employed malicious macros in an Excel spreadsheet, according to Ehud Shamir, chief security officer with SentinelOne, who reverse-engineered a sample of the BlackEnergy 3 malware, the variant used to infect machines at power distribution operation centers in Ukraine. Shamir found that macro-rigged Excel spreadsheets dropped the payload, which included a network sniffer for reconnaissance efforts.

Black Energy 3 is known to be capable of delivering malware via macros.

Shamir said in an earlier interview that the attackers either targeted older unpatched Office systems, or enabled the macros so they would install the malicious code.

Meanwhile, Paul Ducklin, a security evangelist at Sophos, says the new policy option in Office 2016 provides “finer” control over documents with macros. “You can now limit the functionality of the macro programming system so that even if users normally have the chance to enable macros, they can’t if the macros came in an Office file from the internet,” Ducklin said in a recent post.

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