Altair is a GraphQL client for all platforms. From 7.2.4 until 8.5.8, packages/altair-iframe-sandbox/src/main.ts reads plugin_sandbox_opts from the iframe-sandbox query string and passes attacker-controlled scriptUrls to injectScript() in packages/altair-core/src/utils/inject.ts, which creates script elements in the page. The intended parent iframe flow places the page in an iframe with sandbox allow-scripts and without allow-same-origin, but direct navigation to a crafted iframe-sandbox URL omits that isolation and executes the supplied script in the origin serving Altair. Exploitation requires a victim to open the crafted URL, and the resulting script can access script-readable storage and make same-origin requests according to the deployment's authentication and cookie controls. This issue is fixed in version 8.5.8.

Affected: npm: altair-static, npm: altair-express-middleware, npm: altair-koa-middleware, npm: altair-fastify-plugin

### Summary Altair `8.5.7` accepts plugin configuration directly from the `iframe-sandbox` query string.

When `plugin_sandbox_opts` contains `type: "scripts"` and an attacker-controlled URL in `scriptUrls`, the sandbox page creates a classic `<script src="...">` element and loads the supplied script.

In the intended plugin flow, this page runs inside an `<iframe sandbox="allow-scripts">` without `allow-same-origin`, giving plugin code an opaque origin. However, if a victim opens the crafted sandbox URL directly, that iframe isolation is absent and the attacker-controlled script executes in the origin serving Altair, resulting in DOM-based cross-site scripting (XSS) / arbitrary JavaScript execution in the Altair hosting origin.

Exploitation requires the victim to open a crafted URL.

### Details The sandbox reads its configuration directly from `window.location.search`.

In `packages/altair-iframe-sandbox/src/main.ts`:

``` const searchParams = new URLSearchParams(window.location.search); const sandboxType = searchParams.get('sandbox_type');

switch (sandboxType) { case 'plugin': handlePluginSandbox(); break; } ```

`handlePluginSandbox()` then parses `plugin_sandbox_opts`:

``` const searchParams = new URLSearchParams(window.location.search); const pluginSandboxOptsStr = searchParams.get('plugin_sandbox_opts');

const pluginSandboxOpts = pluginSandboxOptsStr ? (JSON.parse(pluginSandboxOptsStr) as PluginParentWorkerOptions) : undefined; ```

The relevant vali…