Description
Drupal 8.4.x versions before 8.4.5 and Drupal 7.x versions before 7.57 has a Drupal.checkPlain() JavaScript function which is used to escape potentially dangerous text before outputting it to HTML (as JavaScript output does not typically go through Twig autoescaping). This function does not correctly handle all methods of injecting malicious HTML, leading to a cross-site scripting vulnerability under certain circumstances. The PHP functions which Drupal provides for HTML escaping are not affected.
Remediation
References
Related Vulnerabilities
WordPress Plugin Visual Form Builder Unspecified Vulnerability (3.0.5)
Plone CMS Permissions, Privileges, and Access Controls Vulnerability (CVE-2015-7317)
Contao Improper Control of Generation of Code ('Code Injection') Vulnerability (CVE-2021-37626)
WebERP Incorrect Permission Assignment for Critical Resource Vulnerability (CVE-2018-20420)