| Package | Affected versions | Patched versions |
|---|---|---|
| league/commonmark | ≥ 1.5.0, < 2.7.0 | 2.7.0 |
Cross-site scripting (XSS) vulnerability in the Attributes extension of the league/commonmark library (versions 1.5.0 through 2.6.x) allows remote attackers to insert malicious JavaScript calls into HTML.
The league/commonmark library provides configuration options such as html_input: 'strip' and allow_unsafe_links: false to mitigate cross-site scripting (XSS) attacks by stripping raw HTML and disallowing unsafe links. However, when the Attributes Extension is enabled, it introduces a way for users to inject arbitrary HTML attributes into elements via Markdown syntax using curly braces.
As a result, even with the secure configuration shown above, an attacker can inject dangerous attributes into applications using this extension via a payload such as:
![](){onerror=alert(1)}
Which results in the following HTML:
<p><img onerror="alert(1)" src="" alt="" /></p>
Which causes the JS to execute immediately on page load.
Version 2.7.0 contains three changes to prevent this XSS attack vector:
on are considered unsafe and blocked by defaulthref and src attributes now respect the existing allow_unsafe_links configuration optionIf upgrading is not feasible, please consider:
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