GHSA-9wjq-cp2p-hrgf: Loofah: SVG `href` attribute bypasses local-reference restriction

Summary Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents. Impact SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk. Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected. Mitigation Upgrade to Loofah >= 2.25.2. Credit Found by the maintainer, Mike Dalessio, during a security audit.