Didier Stevens

Wednesday 6 May 2009

A Very Brief History of Foxit Reader and JavaScript

Filed under: PDF,Vulnerabilities — Didier Stevens @ 23:45

As I often read questions about Foxit Reader and JavaScript support, I decided to write down this very brief history.

Foxit Reader is a lightweight PDF reader, it consist of exactly one EXE file.

Up to Foxit Reader version 2.1, there was no built-in support for JavaScript. If you needed JavaScript, you had to install a plugin (this was actually just a DLL).

Version 2.1 came with builtin JavaScript support. No more plugin, the DLL was merged into the EXE. But the Foxit developers made a design decision with important security implications: you couldn’t disable JavaScript support. Uptil version 2.1, it was easy to disable JavaScript: don’t install the plugin. But with version 2.1, JavaScript was embedded.

Version 2.2 and 2.3 didn’t change this, that’s what prompted me to publish a hack to disable JavaScript.

We had to wait for version 3.0 to be able to disable JavaScript:


But at least, this preference was implemented as it should. Once you disable JavaScript, you get no warnings you’ve disabled JavaScript. This is unlike Adobe Reader:


If you disable JavaScript in Adobe Reader, you’ll be proposed to re-enable it each time you open a PDF document with JavaScript. This is extremely confusing for the average user.

Foxit has started to provide an iFilter. I hope Foxit will never integrate this iFilter in their Foxit Reader setup program, because iFilters increase the attack surface.

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