Blog | G5 Cyber Security

PDF Virus Risk: Are Infected Webpages Still Dangerous?

G5 Cyber Security

TL;DR

Converting a virus-infected webpage to PDF does not guarantee it’s safe. While the conversion process often strips executable code, malicious scripts and embedded objects can sometimes survive, or be re-activated when the PDF is opened. Treat PDFs from untrusted sources with caution.

Understanding the Risks

Webpages contain various elements: text, images, videos, and importantly, code (JavaScript, HTML). Viruses often hide within this code to infect your computer when you visit a compromised website. PDFs can also contain embedded JavaScript and other interactive components.

Why Converting Doesn’t Always Help

  1. Code Survival: Some viruses are written in ways that survive the conversion process. The PDF creator might not remove all potentially harmful elements.
  2. Embedded Objects: Webpages often link to external files (images, videos). These files themselves could be infected and get embedded into the PDF during conversion.
  3. JavaScript Re-activation: PDFs can run JavaScript. If a malicious script is present in the original webpage and survives the conversion, it might execute when you open the PDF.
  4. Exploits: Vulnerabilities exist in PDF readers themselves. A specially crafted PDF could exploit these vulnerabilities even if the original virus code is harmless.

Step-by-Step Guide to Mitigate Risk

  1. Source Verification: Always verify the source of any webpage before converting it to a PDF, especially if you suspect it might be infected. If you don’t trust the website, avoid conversion altogether.
  2. Use Reputable Conversion Tools: Choose well-known and trusted PDF converters (e.g., Adobe Acrobat, online services from reputable companies). Avoid obscure or free tools with unknown security practices.
  3. Scan the PDF: After converting, immediately scan the resulting PDF file with a comprehensive antivirus program. Ensure your antivirus is up to date before scanning. 
    # Example using ClamAV (command line) - Linux/macOS
    clamscan your_pdf_file.pdf
  4. PDF Reader Security Settings: Configure your PDF reader’s security settings to disable JavaScript execution by default. This significantly reduces the risk of malicious scripts running.
    • Adobe Acrobat/Reader: Edit > Preferences > JavaScript. Uncheck “Enable JavaScript”.
    • Other Readers: Check the application’s settings for similar options related to scripting and external content.
  5. Sandbox Environment (Advanced): For highly suspicious PDFs, open them in a sandbox environment (e.g., VirtualBox, Windows Sandbox). This isolates the PDF from your main system, preventing it from causing harm.
  6. Online Virus Scanners: Use multiple online virus scanners to check the PDF file. Different scanners use different detection engines and may identify threats that others miss. (e.g., VirusTotal)

Important Considerations

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