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"><script>alert(2)</script>'>
|-|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.
