Cross-site Scripting (XSS) Affecting php-league-commonmark package, versions <2.3.9-1+deb12u1


Severity

Recommended
0.0
medium
0
10

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Threat Intelligence

EPSS
0.25% (15th percentile)

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  • Snyk IDSNYK-ECHOLATEST-PHPLEAGUECOMMONMARK-18612363
  • published11 Aug 2026
  • disclosed7 Mar 2026

Introduced: 7 Mar 2026

CVE-2026-30838  (opens in a new tab)
CWE-79  (opens in a new tab)

How to fix?

Upgrade Echo:latest php-league-commonmark to version 2.3.9-1+deb12u1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream php-league-commonmark package and not the php-league-commonmark package as distributed by Echo. See How to fix? for Echo:latest relevant fixed versions and status.

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 Base Scores

version 3.1