XS-Leak: Detecting IDs using Portal
Summary: PortSwigger researcher Gareth Heyes demonstrated an XS-Leak technique that uses Chrome's experimental portal tag to detect applications by distinctive element IDs, bypassing the X-Frame-Options header that blocks framing on sites like phpMyAdmin. The proof of concept focuses a portal pointed at a phpMyAdmin-specific ID in the URL hash and fires an onblur alert when it gains focus, with a JavaScript-free variant using CSS :focus and :not selectors to reveal a detection message or trigger a cross-domain request.
What you should know: The technique defeats X-Frame-Options, a header many teams treat as a sufficient defense against framing-based attacks, and the CSS-only version works even for users who have disabled JavaScript.
Read the original at PortSwigger Research ↗
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