TabberNeue vulnerable to Stored XSS through wikitext

Summary

Arbitrary HTML can be inserted into the DOM by inserting a payload into any allowed attribute of the <tabber> tag.

Details

The args provided within the wikitext as attributes to the <tabber> tag are passed to the TabberComponentTabs class: https://github.com/StarCitizenTools/mediawiki-extensions-TabberNeue/blob/3a23b703ce36cfc4128e7921841f68230be4059a/includes/Tabber.php#L76

In TabberComponentTabs, the attributes are validated before being supplied to the Tabs template. https://github.com/StarCitizenTools/mediawiki-extensions-TabberNeue/blob/3a23b703ce36cfc4128e7921841f68230be4059a/includes/Components/TabberComponentTabs.php#L15-L31 However, the validation is insufficient. What Sanitizer::validateTagAttributes does is call validateAttributes, which

	 * - Discards attributes not on the given list
	 * - Unsafe style attributes are discarded
	 * - Invalid id attributes are re-encoded

However, the attribute values are expected to be escaped when inserted into HTML.

The attribute values are then inserted into HTML without being escaped: https://github.com/StarCitizenTools/mediawiki-extensions-TabberNeue/blob/3a23b703ce36cfc4128e7921841f68230be4059a/includes/templates/Tabs.mustache#L1

PoC

XSS through attributes:

1. Go to Special:ExpandTemplates and insert the following wikitext:

<tabber class='test123" onmouseenter="alert(1)"'>
|-|First Tab Title=
First tab content goes here.
</tabber>

2. Press "OK"
3. Hover over the tabber

XSS through script tags:

1. Go to Special:ExpandTemplates and insert the following wikitext:

<tabber class='test123"&gt;&lt;script&gt;alert(2)&lt;/script&gt;'>
|-|First Tab Title=
First tab content goes here.
</tabber>

2. Press "OK"

Impact

Arbitrary HTML can be inserted into the DOM by any user, allowing for JavaScript to be executed.