How do I properly escape quotes inside HTML attributes?

Question

I have a drop down on a web page which is breaking when the value string contains a quote.

The value is \"asd, but in the DOM it always appears as an em

Answer 1

Per HTML syntax, and even HTML5, the following are all valid options:

<option value="&quot;asd">test</option>
<option value="&#34;asd">test</option>
<option value='"asd'>test</option>
<option value='&quot;asd'>test</option>
<option value='&#34;asd'>test</option>
<option value=&quot;asd>test</option>
<option value=&#34;asd>test</option>

Note that if you are using XML syntax the quotes (single or double) are required.

Here's a jsfiddle showing all of the above working.

Answer 2

" is the correct way, the third of your tests:

<option value="&quot;asd">test</option>

You can see this working below, or on jsFiddle.

alert($("option")[0].value);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select>
  <option value="&quot;asd">Test</option>
</select>

Alternatively, you can delimit the attribute value with single quotes:

<option value='"asd'>test</option>

Answer 3

You really should only allow untrusted data into a whitelist of good attributes like: align, alink, alt, bgcolor, border, cellpadding, cellspacing, class, color, cols, colspan, coords, dir, face, height, hspace, ismap, lang, marginheight, marginwidth, multiple, nohref, noresize, noshade, nowrap, ref, rel, rev, rows, rowspan, scrolling, shape, span, summary, tabindex, title, usemap, valign, value, vlink, vspace, width

You really want to keep untrusted data out of javascript handlers as well as id or name attributes (they can clobber other elements in the DOM).

Also, if you are putting untrusted data into a SRC or HREF attribute, then its really a untrusted URL so you should validate the URL, make sure its NOT a javascript: URL, and then HTML entity encode.

More details on all of there here: https://www.owasp.org/index.php/Abridged_XSS_Prevention_Cheat_Sheet

Answer 4

Another option is replacing double quotes with single quotes if you don't mind whatever it is. But I don't mention this one:

<option value='"asd'>test</option>

I mention this one:

<option value="'asd">test</option>

In my case I used this solution.

Answer 5

If you are using Javascript and Lodash, then you can use _.escape(), which escapes ", ', <, >, and &.

See here: https://lodash.com/docs/#escape

Answer 6

If you are using PHP, try calling htmlentities or htmlspecialchars function.