Disallow unsafe HTML templating (no-unsafe-innerhtml)

This function disallows unsafe coding practices that may result into security vulnerabilities. We will disallow assignments to innerHTML as well as calls to insertAdjacentHTML without the use of a pre-defined escaping function. The escaping functions must be called with a template string. The function names are hardcoded as Sanitizer.escapeHTML and escapeHTML.

Rule Details

The rule disallows unsafe coding practices while trying to allow safe coding practices.

Here are a few examples of code that we do not want to allow:

foo.innerHTML = input.value;
bar.innerHTML = "<a href='"+url+"'>About</a>";

A few examples of allowed practices:

foo.innerHTML = 5;
bar.innerHTML = "<a href='/about.html'>About</a>";
bar.innerHTML = escapeHTML`<a href='${url}'>About</a>`;

This rule is being used within Mozilla to maintain and improve the security of the Firefox OS front-end codebase Gaia. Further documentation, which includes references to the escaping functions can be found on MDN.