CVE-2026-30838
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.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
league/commonmarkPackagist | >= 2.0.0, < 2.8.1 | 2.8.1 |
Affected products
3cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*+ 1 more
- cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*range: <2.8.1
- (no CPE)range: < 2.8.1
Patches
Vulnerability mechanics
References
4- github.com/advisories/GHSA-4v6x-c7xx-hw9fghsaADVISORY
- github.com/thephpleague/commonmark/security/advisories/GHSA-4v6x-c7xx-hw9fnvdMitigationVendor AdvisoryWEB
- nvd.nist.gov/vuln/detail/CVE-2026-30838ghsaADVISORY
- commonmark.thephpleague.com/extensions/disallowed-raw-htmlghsaWEB
News mentions
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