GHSA-hh8v-hgvp-g3f5

### Impact

The `DomainFilteringAdapter` in the Embed extension is vulnerable to an allowlist bypass due to a missing hostname boundary assertion in the domain-matching regex. An attacker-controlled domain like `youtube.com.evil` passes the allowlist check when `youtube.com` is an allowed domain.

This enables two attack vectors:

- **SSRF**: The `OscaroteroEmbedAdapter` makes server-side HTTP requests to the embed URL via the `embed/embed` library. A bypassed domain filter causes the server to make outbound requests to an attacker-controlled host, potentially probing internal services or exfiltrating request metadata. - **XSS**: `EmbedRenderer` outputs the oEmbed response HTML directly into the page with no sanitization. An attacker controlling the bypassed domain can return arbitrary HTML/JavaScript in their oEmbed response, which is rendered verbatim.

Any application using the `Embed` extension and relying on `allowed_domains` to restrict domains when processing untrusted Markdown input is affected.

### Patches

This has been patched in version **2.8.2**. The fix replaces the regex-based domain check with explicit hostname parsing using `parse_url()`, ensuring exact domain and subdomain matching only.

### Workarounds

- Disable the `Embed` extension, or restrict its use to trusted users - Provide your own domain-filtering implementation of `EmbedAdapterInterface` - Enable a [Content Security Policy (CSP)](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) and outbound firewall restrictions