CVE-2026-30838

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 v3 6.1 MEDIUM

6.1^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 2.7

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope CHANGED

References

Link	Resource
https://github.com/thephpleague/commonmark/security/advisories/GHSA-4v6x-c7xx-hw9f	Mitigation Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-03-07 16:15

Updated : 2026-06-17 10:33

NVD link : CVE-2026-30838

Mitre link : CVE-2026-30838

CVE.ORG link : CVE-2026-30838

JSON object : View

Products Affected

thephpleague

commonmark

CWE

CWE-79

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

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