Think a File Is Malware? Here’s How to Open It Safely Without Getting Hacked
The Foundation for Press Freedom has an open-source tool that is perfect if you want to consult the inside of a file that you think may be malicious.
A simple click on a file can trigger an infection on your computer that, in the best cases, will affect performance and, in the worst, can lead to the exfiltration of your personal data.
There are numerous tools that already check if the link you are visiting or the file you have downloaded is malicious, such as Virus Total and others that scan thousands and thousands, although none of them will show you the inside of the file.
To do this, it is best to use Dangerzone, an open-source application developed by the Freedom of the Press Foundation (FPF).
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This non-profit organization is responsible for protecting journalism in the public interest and manages other useful tools, such as SecureDrop, used by media such as The Guardian or The New York Times for secure communication with sources.
In this specific case, it is also positioned as a very good tool for those who constantly use spreadsheets, PDF files, or Word documents, as it creates a sandbox or safe environment to visualize what is hidden inside.
This is a must if you work with a lot of client invoices, if you’re a journalist and receive numerous emails with attachments, or simply if you want an extra layer of protection on your computer.
How Dangerzone Works to Open Dangerous Files
Imagine that you are dedicated to checking packages that are delivered to an address, but in all of them there is a probability that there is a type of poison. In case you open the box at once, you could directly poison yourself.
Taking into account this more visual example, Dangerzone takes care of taking photographs of that entire package in an armored space, deletes that original, and builds a copy that the receiver can now consult with total security.
This is a must-have for this type of file, as it can not only contain plain text but also embedded elements, detailed metadata, JavaScript code, and even interactive hyperlinks that can communicate with external servers.
This is where what are also known as “tracking pixels” come into play, so an attacker could receive requests on their own server, directly knowing the IP address, approximate geographical location, and other values such as date, time, and operating system.
DangerZone, on the other hand, takes a zero trust approach, as opposed to the reactive approaches of antivirus and other tools; in other words, it destroys a file but recreates it identically so that the user can access its contents.
In practice, you simply have to download and install it from its official website or on its GitHub page, and run the tool to generate the virtualized environment—it takes just a few seconds.
On its interface you will have a button to upload files. Choose it and upload the file you suspect, without opening it in any other type of application, only with the Danger Zone. Initially, it will boot into a sandbox using an isolated Linux container, regardless of the operating system you have chosen.
Dangerzone, in the second step, performs a conversion to standard PDF, using really familiar applications, such as LibreOffice or PyMuPDF, with the aim of rendering the document and having it in a traditional PDF.
So that the generated file doesn’t have any kind of trace of lines of malicious code, the pages are converted into a huge bitmap with pure RGB pixel data. This complete pixelization is the second step in making the generated file safe for the user.
This pixel data is eventually sent to a second isolation container completely independent of the first, so it doesn’t know where the original file comes from or the original structure; it only receives instructions on colors and visual positioning.
As it is logical that a file of this type is no longer editable or even selectable, DangerZone solves this by optionally running an Optical Character Recognition (OCR) engine called Tesseract.
At the end of this process, the user receives a final file with the suffix “-safe.pdf,” which is the one you can open with total peace of mind to see the contents of the malicious file.
In addition, both containers self-destruct so as not to leave any trace in the computer’s memory, thus eliminating any type of malware that they intended to execute.
In just 1 minute, you’ll have secured your PC without having to mess around with more complicated tools; In case the file is not infected, you will still be able to use it without any problems.
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However, like any application, it also has its limitations. For example, if your PDF file is editable, form-like, or has advanced features, you’ll lose this type of information, as well as transition animations, embedded videos, or review comments.
In addition, the resulting secure file can weigh much more than the original, basically because each page is now a high-resolution compressed image, something that the compression algorithms of the latest versions of the app continue to improve.
Finally, hyperlinks will not appear either, so all links that were embedded in the text will be lost, unless the web address appears directly in the text itself.
FAQ from Content
Q1. What is Dangerzone, and what is it used for?
A1. Dangerzone is a free, open-source application developed by the Freedom of the Press Foundation (FPF). It allows users to safely inspect potentially malicious files by converting them into a secure PDF inside an isolated sandbox environment.
Q2. How does Dangerzone protect my computer from malicious files?
A2. Dangerzone opens suspicious files inside isolated Linux containers, converts them into bitmap images, and creates a new, sanitized PDF. This process removes embedded scripts, macros, JavaScript, metadata, and other potentially harmful content before you open the file.
Q3. Which file types are best suited for Dangerzone?
A3. Dangerzone is especially useful for documents such as PDFs, Microsoft Word files, spreadsheets, and similar document formats that may contain embedded code or hidden tracking elements.
