Cross-Site Scripting in nunjucks

Affected versions of nunjucks do not properly escape specially structured user input in template vars when in auto-escape mode, resulting in a cross-site scripting vulnerability.

Proof of Concept

By using an array for the keys in a template var, escaping is bypassed.

name[]=<script>alert(1)</script>

A full PoC is available in the references section.

Recommendation

Update to version 2.4.3 or later.