CVE-2019-9821: Mozilla Firefox

High severity, CVSS 8.1. EPSS: 0.8% chance of exploitation in the next 30 days.

A use-after-free vulnerability can occur in AssertWorkerThread due to a race condition with shared workers. This results in a potentially exploitable crash. This vulnerability affects Firefox < 67.

Affected products

• Mozilla Firefox: before 67.0 (fixed in 67.0)

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