Malware in Zips: Can it Run?

TL;DR

Yes, malware can execute from within a zipped file, but not directly. It relies on tricks to get you or your system to extract and run the malicious content. Modern operating systems have protections, but staying vigilant is key.

How Malware Hides in Zips

Zipped files themselves aren’t executable. However, they can contain executable files (like .exe, .bat, .scr) or other file types that lead to execution. Here’s how it works:

Steps to Protect Yourself

1. Be Careful with Attachments: The most common way malware spreads via zips is through email attachments. Never open zip files from unknown senders or if the email looks suspicious, even if it appears to be from someone you know.
2. Scan Before Opening: Always scan any zip file with a reputable antivirus program before extracting its contents. Most modern antivirus software will automatically do this when you try to open a zip.
   • Example using Windows Security (scan a folder):

     powershell -Command "Get-MpComputerStatus | Select-Object AntivirusEnabled, RealTimeProtectionEnabled"

     This checks if your antivirus is running.

3. File Extensions Matter: Pay attention to the file extensions inside the zip. Be wary of double extensions (e.g., document.txt.exe). This attempts to disguise an executable as a harmless text file.
   • Windows often hides known extensions by default. Enable ‘Show file name extensions’ in File Explorer options (View tab) to see the full extension.
4. Beware of Office Documents with Macros: Zips frequently contain Microsoft Office documents (.doc, .xls, .ppt) that have malicious macros embedded within them. Disable macros by default in your Office settings and only enable them if you absolutely trust the source.
   • In Excel/Word/PowerPoint: File > Options > Trust Center > Trust Center Settings > Macro Settings. Choose ‘Disable all macros with notification’ or ‘Disable all macros without notification’.
5. Script Files (.bat, .ps1): Be extremely cautious of script files within zips. These can execute commands on your system.
   • Avoid running batch scripts from untrusted sources.
6. Archive Bombs: While less common now, archive bombs are zips designed to exhaust system resources when extracted. Antivirus software usually detects these.
7. Sandboxing (Advanced): For highly suspicious files, consider extracting them in a virtual machine or sandbox environment. This isolates the potential malware from your main system.
   Example using Windows Sandbox:

   sandboxcmd

What Happens When You Extract?

When you extract a zip file containing malicious content, one of these things might happen:

• Direct Execution: If the zip contains an executable file and your system is configured to automatically run executables, it could launch immediately.
• Social Engineering: The zip might contain a document that prompts you to ‘Enable Content’ (macros) or open a link leading to a malicious website.
• Exploit Kits: Some zips contain files designed to exploit vulnerabilities in your software when opened.

Modern Protections

Operating systems like Windows have built-in protections:

• SmartScreen Filter: Warns you about potentially dangerous executables downloaded from the internet.
• User Account Control (UAC): Prompts for permission before running programs that require administrative privileges.

However, these protections aren’t foolproof and can be bypassed with clever techniques.

cyber security Best Practices

Regularly update your operating system, antivirus software, and other applications to patch vulnerabilities. Be skeptical of unsolicited emails and attachments, and always think before you click!