CVE-2020-35112: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 1.3% chance of exploitation in the next 30 days.

If a user downloaded a file lacking an extension on Windows, and then "Open"-ed it from the downloads panel, if there was an executable file in the downloads directory with the same name but with an executable extension (such as .bat or .exe) that executable would have been launched instead. *Note: This issue only affected Windows operating systems. Other operating systems are unaffected.*. This vulnerability affects Firefox < 84, Thunderbird < 78.6, and Firefox ESR < 78.6.

Affected products

• Mozilla Firefox: before 84.0 (fixed in 84.0)
• Mozilla Firefox ESR: before 78.6.0 (fixed in 78.6.0)
• Mozilla Thunderbird: before 78.6.0 (fixed in 78.6.0)

Published 2021-01-07. Last modified 2026-06-17.