CVE-2021-23995

high
Published — · Modified —
CVSS v3
CVSS v2
VIR risk
8.0

Description

When Responsive Design Mode was enabled, it used references to objects that were previously freed. We presume that with enough effort this could have been exploited to run arbitrary code. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.

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-2021-23995

vendor Authored 2026-05-27

Vendor advisory: suse — https://www.suse.com/security/cve/CVE-2021-23995.html

vendor Authored 2026-05-27

Vendor advisory: arch — https://security.archlinux.org/ASA-202104-3

vendor Authored 2026-05-27

Vendor advisory: arch — https://security.archlinux.org/ASA-202104-4

OS impact

OSVersionStatusFixed in
arch archfixed78.10.0-1
suse slesaffected
debian debiansidfixed88.0-1
debian debianbookwormfixed78.10.0esr-1
debian debianbullseyefixed78.10.0esr-1
debian debianforkyfixed78.10.0esr-1
debian debiantrixiefixed78.10.0esr-1

References

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