Script-based malware. How to stay protected?

Script-Based Malware
Script-Based Malware

Over the last four years, the share of script-based attacks of malware offenses worldwide has grown so drastically that it raised alerts among security specialists and ordinary users. In this post, we shall regard script-based malware, assess its strengths and weaknesses, explain how the attacks happen, and suggest measures to maintain security in your workgroup.

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What is script-based malware?

To understand how someone can run a script-based attack on a computer, we must know what scripts are. They are sets of commands for a system to execute. Users employ them to automatize processes that they would otherwise perform manually. Programmers and advanced users create scripts in scripting languages. Those can be, roughly speaking, general-purpose (such as JavaScript, Python, and PHP), OS-oriented (like PowerShell and AppleScript), and there are also special script languages for particular applications and environments.

PowerShell Window
PowerShell is a handy Windows automation tool and a suitable environment for script-based attacks.

The scripts are neither malicious files nor the main content of files they inhabit. Instead, they are the documents’ allowable components, legal and, in theory, beneficial to the user. Scripts are not compiled. That means they are interpreted and executed by the software environment ad hoc without previous translation into machine code. For AppleScript, for example, such an environment is an Apple operating system. And for cross-system JavaScript (if it is about website construction), any modern web browser can serve as an interpreting environment.

The script-based hacker attacks are obviously the cyber-crimes that use scripts as a primary tool.

Related: “Malware” vs. “virus”.

What is so worrying about the script-based attacks?

First of all, scripts are not files, as we already mentioned. Antivirus programs have a hard time detecting them, or better to say: they are useless against scripts. It is so because modern security software focuses on detecting and removing malicious files. Thus, in the case of script-based attacks, we are dealing with ghostly malware, invisible to antivirus programs.

Another important thing is that scripts are generally hard to detect. They exist in primary memory, soon to be overwritten or erased. It is actually possible to find the origin of a script if criminals inaccurately leave traces, but why would they do that.

How can an attacker execute malware through a script?

Let’s make it clear: we are not talking about malicious scripts tied to websites (Cross-Site Scripting), which are more or less studied and covered by browser and antivirus security systems. Files fitted with simple yet treacherous scripts constitute a new problem. These are the files whose formats antivirus software lets through by default, not regarding as dangerous: PDF, Word, e-books, HTML applications, and others.

Simple JavaScript code usually employed in files like these can add various practical functions, like making PDF documents signable or featuring a fillable questionnaire. But the script can have a malicious purpose as well. In case of a script-based attack, it most likely will be a set of commands to download any other malware that harms for real. Ransomware, for instance, is the most lucrative type of attack for hackers. The crooks only expect a user to open a file to run the script or, in some cases, to allow macros therefor.

Disabled Macros in Word
RED FLAG: a downloaded document asks you to enable macros in MS Office.

Script-stuffed files can also be downloaded items you are trusty about since they update programs you already have. At least, you believe so. These can be plug-ins, add-ons, and so on. Yes, the UAC will ask whether you really want to download this file, but this always happens, and we tend to ignore such warnings. If the criminals manage to cheat you – consider they also cheated your security software. By the way, various untrustworthy PDF-readers and their plug-ins are one of the most dangerous programs in terms of script-based attack menace.

The script-based attacks mostly endanger Windows systems exploiting vulnerabilities of Command Prompt and PowerShell, the in-built automation tools. However, neither Android, iOS, nor even Linux is safe.

How to protect yourself and your workgroup?

The weakness of script-based malware is that it has to be run by the user. Therefore, the best protection is to be cautious and avoid unknown downloads. Remember that PDF, Word, and other data files can contain a malicious script. These bogus files are most likely to arrive via e-mail or messengers in letters sent seemingly by someone you trust – usually services-providing organizations. Be especially wary of reports from delivery companies like FedEx. Since a postal delivery is pretty believable to be unexpected, hackers often use this disguise for their phishing mail. Before downloading any attachments from suspicious senders, triple-check the source and the message itself. If you are attentive enough, you will find a mistake in the address line, your name, or the text itself.

Email with a PDF attachment
Watch out for dubious e-mails with enclosed PDF files, Word documents, HTML application, etc.

In workgroups, it makes sense to separate those computers that need to run scripts from those that can do without them. The former should maintain extreme vigilance and advisably deploy zero-trust policy antivirus software, which is for the moment presented by Windows 11 Defender. It has many issues, but it seriously jeopardizes the plans of malefactors who go in for script-based attacks.

Script-fitted files can spread rapidly via the injured network using the same vulnerabilities of Windows elements they use to deliver their malicious payload. General security measures, such as file backup and network separation, are also a must to minimize the destructive effect of any successful cyber-attack.

Consider reading: Slow PC. Possible causes and how to fix them.

By Stephanie Adlam

I write about how to make your Internet browsing comfortable and safe. The modern digital world is worth being a part of, and I want to show you how to do it properly.

View all of Stephanie Adlam's posts.

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