CVE-2020-26961

critical
Published — · Modified —
CVSS v3
CVSS v2
VIR risk
9.5

Description

When DNS over HTTPS is in use, it intentionally filters RFC1918 and related IP ranges from the responses as these do not make sense coming from a DoH resolver. However when an IPv4 address was mapped through IPv6, these addresses were erroneously let through, leading to a potential DNS Rebinding attack. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

Predictions

Exploit likelihood
20%
Patch ETA

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

vendor Authored 2026-05-27

Vendor advisory: debian — https://security-tracker.debian.org/tracker/CVE-2020-26961

vendor Authored 2026-05-27

Vendor advisory: suse — https://www.suse.com/security/cve/CVE-2020-26961.html

vendor Authored 2026-05-27

Vendor advisory: arch — https://security.archlinux.org/ASA-202011-12

OS impact

OSVersionStatusFixed in
arch archfixed83.0-1
suse slesaffected
debian debiansidfixed83.0-1
debian debianbookwormfixed78.5.0esr-1
debian debianbullseyefixed78.5.0esr-1
debian debianforkyfixed78.5.0esr-1
debian debiantrixiefixed78.5.0esr-1

References

Verify integrity in audit chain (admin only). AS-IS.