mediawiki/maps has stored XSS through the overlays parameter in the display_map parser function

Summary

Stored XSS through wikitext can be performed by inserting malicious HTML into the overlays parameter of the display_map parser function when using the leaflet service.

Details

The maps extension doesn't escape overlay names before passing them to leaflet. Leaflet then inserts them as HTML: https://github.com/ProfessionalWiki/Maps/blob/ca5139fabd75f3c34f47ea3fd161306506b053bc/resources/lib/leaflet/leaflet.js#L5243

PoC

Preview the following wikitext, using the default configuration options of the extension:

{{#display_map:0,0|service=leaflet|overlays=OpenTopoMap.<img src=x onerror="alert(1);">}}

Impact

Stored XSS can be performed by any user with the edit permission.