Citizen vulnerable to Stored XSS through short descriptions

Summary

Short descriptions set via the ShortDescription extension are inserted as raw HTML by the Citizen skin, allowing any user to insert arbitrary HTML into the DOM by editing a page.

Details

The shortdesc property, which contains unsanitized user input, is retrieved from the OutputPage and returned as the tagline: https://github.com/StarCitizenTools/mediawiki-skins-Citizen/blob/0d8a44011e02a081618359a1e90f462478e807aa/includes/Components/CitizenComponentPageHeading.php#L249-L251 The tagline is then provided to the template data: https://github.com/StarCitizenTools/mediawiki-skins-Citizen/blob/0d8a44011e02a081618359a1e90f462478e807aa/includes/Components/CitizenComponentPageHeading.php#L270-L275 The template then inserts the tagline into raw HTML without doing any escaping: https://github.com/StarCitizenTools/mediawiki-skins-Citizen/blob/0d8a44011e02a081618359a1e90f462478e807aa/templates/PageHeading.mustache#L12

PoC

1. Enable Citizen and ShortDescription
2. Add {{SHORTDESC:<img src="" onerror="alert('citizen shortdescription xss')">}} to a page
3. Visit the page

Impact

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