CVE-2020-26976

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.6% 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 a HTTPS pages was embedded in a HTTP page, and there was a service worker registered for the former, the service worker could have intercepted the request for the secure page despite the iframe not being a secure context due to the (insecure) framing. This vulnerability affects Firefox < 84.

Affected products

Debian Linux: 9.0, 10.0
Mozilla Firefox: before 84.0 — fixed in 84.0

How to fix

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

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1674343
https://lists.debian.org/debian-lts-announce/2021/02/msg00001.html
https://lists.debian.org/debian-lts-announce/2021/02/msg00002.html
https://security.gentoo.org/glsa/202102-02
https://www.debian.org/security/2021/dsa-4840
https://www.debian.org/security/2021/dsa-4842
https://www.mozilla.org/security/advisories/mfsa2020-54/
https://bugzilla.mozilla.org/show_bug.cgi?id=1674343
https://lists.debian.org/debian-lts-announce/2021/02/msg00001.html
https://lists.debian.org/debian-lts-announce/2021/02/msg00002.html
https://security.gentoo.org/glsa/202102-02
https://www.debian.org/security/2021/dsa-4840

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