GHSA-hh8v-hgvp-g3f5 league/commonmark has an embed extension allowed_domains bypass

• Packagist league/commonmark: >= 2.3.0, < 2.8.2 → fixed in 2.8.2

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) and outbound firewall restrictions