Hardening Adobe Reader

PDF files have become commonplace on the Internet and in the business world, but they have also become favorite tools for attackers to deliver malicious payloads. While some problems may be mitigated by using an alternative PDF reader, many people have little choice but to use the standard Adobe Reader. In that situation, you can help protect yourself from many PDF-based attacks by following a few basic steps.

1. Make sure you have an up-to-date anti-malware program installed and running with automatic download of new virus definitions. Older tools may not scan for recent PDF-based threats.
2. Make sure you have the latest version of Adobe Reader. Enable automatic updates by opening Reader and choosing Edit > Preferences > Updater. Adobe regularly issues patches against new vulnerabilities.
3. Disable JavaScript in PDF files. This may affect certain features at times, such as PDF-based forms, but it’s better to enable JavaScript only when needed. In Reader, click Edit > Preferences > JavaScript and uncheck the box for “Enable Acrobat JavaScript.”
4. Disable Flash and multimedia in PDF files. Once again, this may prevent a few documents from loading some content, but embedded Flash is a common tool for exploiting Reader. Go to Edit > Preferences > Multimedia Trust (legacy) and either uncheck “Allow multimedia operations” or change the permissions on each listed player to “Prompt.” Be sure to check the settings for both trusted documents and other documents by changing the “Display Permissions for” option.
5. Disable attachments. Earlier this year, security researcher Didier Stevens uncovered a PDF behavior that could be used to launch commands outside of Reader. To avoid this problem, open Edit > Preferences > Trust Manager and uncheck the box marked “Allow opening of non-PDF file attachments with external applications.”
6. Configure your browser to show a download prompt for PDF files. The exact settings for this step will depend on your browser. Remove any plug-ins or add-ons for Adobe Reader, and check the settings for how your browser handles various file formats to check the behavior for PDF files. If you allow PDF files to open in the browser or open in Reader automatically, you may accidentally open a malicious file without realizing it.

These precautions are only a small part of keeping your computer protected against attack, but they will go a long way to help you avoid many threats involving PDF files.