Turndown input is

• either a string that is passed to a DOM parser
• or an HTMLElement referring to an already built DOM tree

When a string input is passed, the DOM parser is picked as follows.

• For web browser usage, the corresponding native web parser is used, which is typically DOMImplementation.
• For standalone usage, custom domino parser is used.

Please note that a malicious string input can cause undesired effects within the DOM parser even before Turndown code starts processing the document itself. These effects especially include script execution and downloading external resources.

For critical applications with untrusted inputs, you should consider either cleaning up the input with a dedicated HTML sanitizer library or using an alternate DOM parser that better suits your security needs.

In particular, Turndown version 6 and below used jsdom as the standalone DOM parser. As jsdom is a fully featured DOM parser with script execution support, it imposes an inherent security risk. We recommend upgrading to version 7, which uses custom domino that doesn't even support executing scripts nor downloading external resources.

If you've found a vulnerability, please report it to disclosure@orchitech.cz and we'll get back to you.