Malware that can get past your Anti-Virus Scanner…

There is a new technique Cyber-thugs are using to attack Internet users that allows Malware to get past your Anti-Virus Scanner. This article was e-mailed to me on Wednesday, February 14, 2018. It comes from CyberHeist News, a research firm in cyber security.

According to researchers at McAfee, a new malware campaign is targeting organizations associated with the upcoming 2018 Winter Olympics in Pyeongchang, South Korea. This new technique is expected to make it into your users’ inbox soon, so here is your heads-up.

The attack is being delivered via phishing emails disguised as alerts from the country’s National Counter-Terrorism Center, with malicious Word documents attached. Future attacks could be using any social engineering tricks.

Jonathan, from our friends at Barkly, explained the technical background: “Once opened, the Word doc encourages readers to enable content. If they do, that triggers an embedded macro to launch PowerShell. Up to this point, this is nothing really new.

But here’s where things get interesting…

Why this attack is different: What truly makes this campaign notable is its use of a brand new PowerShell tool called Invoke-PSImage that allows attackers to hide malicious scripts in the pixels of otherwise benign-looking image files, and later execute them directly from memory.

Why that’s dangerous: Not only does hiding the script inside an image file help it evade detection, executing it directly from memory is a “file-less” technique (not executed from a file the scanner reads) that generally won’t get picked up by traditional antivirus solutions.

No download necessary: Invoke-PSImage can be used to extract scripts from downloaded images or images hosted on the web. That means an attacker doesn’t necessarily need to download an image onto a machine in order to get a script embedded inside it to run on that machine.

In the case of this particular malware campaign, the image file is downloaded to the victim’s machine. Once extracted, the embedded script is passed to the Windows command line and executed via PowerShell.

This attack is another troubling example of how attacks are evolving away from using malicious .exe’s.

In the past, we’ve seen many attacks abusing PowerShell follow a tried-and-true pattern:

Spam email with Word attachment > Word attachment with embedded macro > Macro launches PowerShell script > PowerShell script downloads and executes malware .exe payload

In these scenarios, traditional antivirus solutions have a chance of scanning and blocking the attack, but not until the very last step. Once the malware payload has been downloaded onto the device the AV might be able to block it, but only if the malware has been seen before and the AV has a signature it can refer to in order to identify it. In these scenarios, we’ve seen plenty of instances where the AV misses and the infection is successful.

This new malware campaign presents an even worse scenario in which the AV doesn’t have that opportunity:

Spam email with Word attachment > Word attachment with embedded macro > Macro launches PowerShell script > PowerShell script extracts 2nd PowerShell script from image and executes it from memory > In-memory executed script gives attacker remote access and control

With no malicious executable file to scan, this attack can easily succeed unless other protections are in place. Here are a few things you can do to reduce your risk of attacks like this:

  • Train employees not to open email attachments from senders they don’t know: They should be especially wary of Word documents that ask them to enable content/macros.
  • Enforce stricter macro controls: For starters, consider blocking macros in Office files downloaded from the internet.
  • Disable or restrict PowerShell: If PowerShell isn’t being used for something vital on a machine, disable it. If it is being used for something vital, consider using PowerShell Constrained Language Mode. That will limit PowerShell to its most basic functionality and make many file-less attack techniques unusable.”

We could not agree more! You need to create a security culture in your organization and these suggestions are important controls. This post is also at the KnowBe4 Blog, at the end it shows a great new way to create a security culture – at no cost:

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