CVE-2019-9820: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 1.6% chance of exploitation in the next 30 days.

A use-after-free vulnerability can occur in the chrome event handler when it is freed while still in use. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 60.7, Firefox < 67, and Firefox ESR < 60.7.

Affected products

• Mozilla Firefox: before 67.0 (fixed in 67.0)
• Mozilla Firefox ESR: before 60.7 (fixed in 60.7)
• Mozilla Thunderbird: before 60.7.0 (fixed in 60.7.0)

Published 2019-07-23. Last modified 2026-06-17.