What’s Vulnerable › Vulnerabilities

CVE-2020-35111

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-01-07 · updated 2026-06-17

Description

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

How to fix

Upgrade to a fixed version: Mozilla Firefox 84.0; Mozilla Firefox ESR 78.6.0; Mozilla Thunderbird 78.6.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1657916
• https://www.mozilla.org/security/advisories/mfsa2020-54/
• https://www.mozilla.org/security/advisories/mfsa2020-55/
• https://www.mozilla.org/security/advisories/mfsa2020-56/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1657916
• https://www.mozilla.org/security/advisories/mfsa2020-54/
• https://www.mozilla.org/security/advisories/mfsa2020-55/
• https://www.mozilla.org/security/advisories/mfsa2020-56/

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