CVE-2020-35111: Mozilla Firefox

Medium severity, CVSS 4.3. EPSS: 1.4% chance of exploitation in the next 30 days.

When an extension with the proxy permission registered to receive <all_urls>, the proxy.onRequest callback was not triggered for view-source URLs. While web content cannot navigate to such URLs, a user opening View Source could have inadvertently leaked their IP address. 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.