CVE-2019-11763: Canonical Ubuntu Linux

Medium severity, CVSS 6.1. EPSS: 1.2% chance of exploitation in the next 30 days.

Failure to correctly handle null bytes when processing HTML entities resulted in Firefox incorrectly parsing these entities. This could have led to HTML comment text being treated as HTML which could have led to XSS in a web application under certain conditions. It could have also led to HTML entities being masked from filters - enabling the use of entities to mask the actual characters of interest from filters. This vulnerability affects Firefox < 70, Thunderbird < 68.2, and Firefox ESR < 68.2.

Affected products

• Canonical Ubuntu Linux: version 16.04 only
• Mozilla Firefox: before 70.0 (fixed in 70.0)
• Mozilla Firefox ESR: before 68.2 (fixed in 68.2)
• Mozilla Thunderbird: before 68.2 (fixed in 68.2)

Published 2020-01-08. Last modified 2026-06-17.