CVE-2026-126362

## Summary The `@astrojs/svelte` renderer wraps slotted content passed to Svelte components in an `<astro-slot>` element, and writes the slot name into its `name` attribute without HTML escaping. A slot name containing `"` could end the attribute and inject arbitrary HTML into the page. For example, a page that takes a slot name from the request: ```astro --- import Tabs from '../components/Tabs.svelte'; const tab = Astro.url.searchParams.get('tab'); --- <Tabs client:load active={tab}><div slot={tab}>…</div></Tabs> ``` rendered with a Svelte 5 component that renders its snippets by name: ```svelte <script> let { active, ...snippets } = $props(); </script> {@render snippets[active]?.()} ``` would output a `tab` value such as `x"><img src=x onerror=alert(1)>` as live HTML. ## Impact Reflected cross-site scripting. An attacker who gets a user to open a crafted link can run JavaScript on the site's origin, but only in applications where all of the following are true: - The page passes request-controlled input (such as a query parameter) as a slot name. - The Svelte component is hydrated with a `client:*` directive. For non-hydrated components the slot wrapper is removed from the output, together with its `name` attribute. - The Svelte component renders the attacker-chosen slot, which in practice means a Svelte 5 component that renders snippets by a dynamic name. Components that never render the slot only output Astro's already escaped fallback template. This is the `@astrojs/svelte` counterpart of GHSA-8hv8-536x-4wqp (CVE-2026-50146), which fixed the same issue in `astro` core. The same unescaped value was also used when hydrating the component in the browser. ## Affected versions `@astrojs/svelte` >= 5.7.3, <= 9.1.1. ## Patches Fixed in `@astrojs/svelte` 9.1.2. Slot names are now HTML-escaped in the server renderer and in the client-side hydration code. ## Workarounds Upgrade to `@astrojs/svelte` 9.1.2 or later. Before upgrading, do not use request-con