CVE-2019-9815: Mozilla Firefox

High severity, CVSS 8.1. EPSS: 1.8% chance of exploitation in the next 30 days.

If hyperthreading is not disabled, a timing attack vulnerability exists, similar to previous Spectre attacks. Apple has shipped macOS 10.14.5 with an option to disable hyperthreading in applications running untrusted code in a thread through a new sysctl. Firefox now makes use of it on the main thread and any worker threads. *Note: users need to update to macOS 10.14.5 in order to take advantage of this change.*. 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 (fixed in 60.7)

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