GHSA-6q87-84jw-cjhp

### Summary

Unsanitized search param names cause XSS vulnerability. You are affected if you iterate over all entries of `event.url.searchParams` inside a server `load` function. Attackers can exploit it by crafting a malicious URL and getting a user to click a link with said URL.

### Details

SvelteKit tracks which parameters in `event.url.searchParams` are read inside server `load` functions. If the application iterates over the these parameters, the `uses.search_params` array included in the boot script (embedded in the server-rendered HTML) will have any search param name included in unsanitized form.

`packages/kit/src/runtime/server/utils.js:150` has the `stringify_uses(node)` function which prints these out.

### Reproduction

In a `+page.server.js` or `+layout.server.js`:

```js /** @type {import('@sveltejs/kit').Load} */ export function load(event) { const values = {};

for (const key of event.url.searchParams.keys()) { values[key] = event.url.searchParams.get(key); } } ```

If a user visits the page in question via a link containing `?</script/><script>window.pwned%3D1</script/>`, the `</script>` will be included verbatim in the payload, causing the embedded script to be executed.

It is not necessary to return the parameter value from `load` or render it in the page, only to read it (which causes it to be tracked as a dependency) while `load` is running.

### Impact

Any application that iterates over all values in `event.url.searchParams` in a `load` function in `+page.server.js` or `+layout.server.js` (directly or indirectly) is vulnerable to XSS.