I frequent a smaller wiki and noticed somebody in the last few hours made a few edits and uploads that are quite suspicious. I haven't viewed these pages myself because of that. Some other people have told me they're attempting to script across domains. The software version is 1.23.4 (released about 5 years ago now) so we all think this may be a legitimate threat.
Topic on Project:Support desk
Okay actually, people are confirming/have confirmed that no xss execution occurs. Whoever tried attacking us did terrible.
MediaWiki 1.23 is old and insecure. Even if this attack did not succeed, you're at risk. Please upgrade to a supported MediaWiki version.