CVE-2026-77606: Semantic MediaWiki has reflected XSS in Special:Ask plain table headers

Failure mode

When headers=plain, table header text was emitted into <th> via a raw HTML path. User-controlled mainlabel content could therefore become executable HTML.

Remediation

• TableResultPrinter now applies output-context escaping before passing plain headers to the table renderer.
• The fix is limited to the HTML/plain-header branch so safe rendering modes are unaffected.

Why this is the right layer

The header value is not a structural token; it is display data. Sanitizing it at the sink is correct because the renderer owns the final HTML emission.