GHSA-4g3v-8h47-v7g6: Astro: Reflected XSS via unescaped View Transition animation properties

Astro’s server-side View Transition CSS generator interpolates animation properties into an inline <style> element without escaping them for the CSS and HTML contexts.

An attacker-controlled value passed to an animation property such as duration can contain a </style> sequence, terminate the generated style element, and inject arbitrary HTML or JavaScript.

This is similar to GHSA-8hv8-536x-4wqp, but exploits a different injection point: unescaped View Transition animation values in a server-generated <style> element rather than an unescaped slot name in a hydration template.

Like GHSA-8hv8-536x-4wqp, exploitation requires an application to pass attacker-controlled data to an Astro API. However, the value is subsequently inserted into the HTML response without context-appropriate escaping by Astro.