{"id":"GHSA-hh8v-hgvp-g3f5","summary":"league/commonmark has an embed extension allowed_domains bypass","details":"### Impact\n\nThe `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.\n\nThis enables two attack vectors:\n\n- **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.\n- **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.\n\nAny application using the `Embed` extension and relying on `allowed_domains` to restrict domains when processing untrusted Markdown input is affected.\n\n### Patches\n\nThis 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.\n\n### Workarounds\n\n- Disable the `Embed` extension, or restrict its use to trusted users\n- Provide your own domain-filtering implementation of `EmbedAdapterInterface`\n- Enable a [Content Security Policy (CSP)](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) and outbound firewall restrictions","aliases":["CVE-2026-33347"],"modified":"2026-03-27T22:16:22.177735Z","published":"2026-03-19T19:04:24Z","database_specific":{"cwe_ids":["CWE-185","CWE-79","CWE-918"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-03-19T19:04:24Z","nvd_published_at":"2026-03-24T20:16:29Z"},"references":[{"type":"WEB","url":"https://github.com/thephpleague/commonmark/security/advisories/GHSA-hh8v-hgvp-g3f5"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33347"},{"type":"WEB","url":"https://github.com/thephpleague/commonmark/commit/59fb075d2101740c337c7216e3f32b36c204218b"},{"type":"PACKAGE","url":"https://github.com/thephpleague/commonmark"},{"type":"WEB","url":"https://github.com/thephpleague/commonmark/releases/tag/2.8.2"}],"affected":[{"package":{"name":"league/commonmark","ecosystem":"Packagist","purl":"pkg:composer/league/commonmark"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.3.0"},{"fixed":"2.8.2"}]}],"versions":["2.3.0","2.3.1","2.3.2","2.3.3","2.3.4","2.3.5","2.3.6","2.3.7","2.3.8","2.3.9","2.4.0","2.4.1","2.4.2","2.4.3","2.4.4","2.5.0","2.5.1","2.5.2","2.5.3","2.6.0","2.6.1","2.6.2","2.7.0","2.7.1","2.8.0","2.8.1"],"database_specific":{"last_known_affected_version_range":"\u003c= 2.8.1","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/03/GHSA-hh8v-hgvp-g3f5/GHSA-hh8v-hgvp-g3f5.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N"}]}