What’s Vulnerable › Vulnerabilities
CVE-2026-30838: league/commonmark: DisallowedRawHtml extension bypass via whitespace in HTML tag names
- Severity: medium (CVSS 6.1 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-03-07 · updated 2026-06-17
- Weakness: CWE-79
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.
Affected products
- thephpleague commonmark: before 2.8.1 — fixed in 2.8.1
How to fix
Upgrade to a fixed version: thephpleague commonmark 2.8.1. Check the vendor advisory for mitigations.
References
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