CVE-2026-63135: YOURLS has stored XSS in referrer statistics chart via crafted Referer header

YOURLS stores the HTTP Referer header for short URL redirects and later renders aggregated referrer domains in the per-link statistics page. An unauthenticated attacker can send a crafted Referer header to any existing short URL. When an authenticated administrator or stats-page viewer opens that short URL’s statistics page, the crafted referrer is embedded into Google Charts JavaScript without JavaScript-string escaping, causing stored cross-site scripting.

This is reachable in default private installations when authenticated users view stats, and in documented configurations where YOURLS_PRIVATE_INFOS is set to false to make statistics pages public.