CVE-2017-7821: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 2% chance of exploitation in the next 30 days.

A vulnerability where WebExtensions can download and attempt to open a file of some non-executable file types. This can be triggered without specific user interaction for the file download and open actions. This could be used to trigger known vulnerabilities in the programs that handle those document types. This vulnerability affects Firefox < 56.

Affected products

• Mozilla Firefox: up to and including 55.0.3

Published 2018-06-11. Last modified 2026-06-17.