Vulnerability Description
league/commonmark is a PHP Markdown parser. Prior to version 2.8.1, the DisallowedRawHtml extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowed HTML tag name and the closing >. For example, <script\n> would pass through unfiltered and be rendered as a valid HTML tag by browsers. This is a cross-site scripting (XSS) vector for any application that relies on this extension to sanitize untrusted user input. All applications using the DisallowedRawHtml extension to process untrusted markdown are affected. Applications that use a dedicated HTML sanitizer (such as HTML Purifier) on the rendered output are not affected. This issue has been patched in version 2.8.1.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Thephpleague | Commonmark | < 2.8.1 |
Related Weaknesses (CWE)
References
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-4v6x-c7xx-hwMitigationVendor Advisory
FAQ
What is CVE-2026-30838?
CVE-2026-30838 is a vulnerability with a CVSS score of 6.1 (MEDIUM). league/commonmark is a PHP Markdown parser. Prior to version 2.8.1, the DisallowedRawHtml extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowe...
How severe is CVE-2026-30838?
CVE-2026-30838 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-2026-30838?
Check the references section above for vendor advisories and patch information. Affected products include: Thephpleague Commonmark.