CVE-2019-9809: Mozilla Firefox

High severity, CVSS 7.5. EPSS: 1.6% chance of exploitation in the next 30 days.

If the source for resources on a page is through an FTP connection, it is possible to trigger a series of modal alert messages for these resources through invalid credentials or locations. These messages cannot be immediately dismissed, allowing for a denial of service (DOS) attack. This vulnerability affects Firefox < 66.

Affected products

• Mozilla Firefox: before 66.0 (fixed in 66.0)

Published 2019-04-26. Last modified 2026-06-17.