Vulnerability Description
league/commonmark is a PHP Markdown parser. From version 2.3.0 to before version 2.8.2, 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 issue has been patched in version 2.8.2.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Thephpleague | Commonmark | >= 2.3.0, < 2.8.2 |
Related Weaknesses (CWE)
References
- https://github.com/thephpleague/commonmark/commit/59fb075d2101740c337c7216e3f32bPatch
- https://github.com/thephpleague/commonmark/releases/tag/2.8.2ProductRelease Notes
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-hh8v-hgvp-g3MitigationVendor Advisory
FAQ
What is CVE-2026-33347?
CVE-2026-33347 is a vulnerability with a CVSS score of 6.1 (MEDIUM). league/commonmark is a PHP Markdown parser. From version 2.3.0 to before version 2.8.2, the DomainFilteringAdapter in the Embed extension is vulnerable to an allowlist bypass due to a missing hostname...
How severe is CVE-2026-33347?
CVE-2026-33347 has been rated MEDIUM with a CVSS base score of 6.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-33347?
Check the references section above for vendor advisories and patch information. Affected products include: Thephpleague Commonmark.