CVE-2016-9909: HTML5LIB

Medium severity, CVSS 6.1. EPSS: 2.2% chance of exploitation in the next 30 days.

The serializer in html5lib before 0.99999999 might allow remote attackers to conduct cross-site scripting (XSS) attacks by leveraging mishandling of the < (less than) character in attribute values.

Affected products

• HTML5LIB HTML5LIB: up to and including 0.99999999

Published 2017-02-22. Last modified 2026-06-17.