CVE-2021-23984

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

Description

A malicious extension could have opened a popup window lacking an address bar. The title of the popup lacking an address bar should not be fully controllable, but in this situation was. This could have been used to spoof a website and attempt to trick the user into providing credentials. This vulnerability affects Firefox ESR < 78.9, Firefox < 87, and Thunderbird < 78.9.

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-2021-23984

vendor Authored 2026-05-27

Vendor advisory: suse — https://www.suse.com/security/cve/CVE-2021-23984.html

OS impact

OSVersionStatusFixed in
arch archfixed78.9.0-1
suse slesaffected
debian debiansidfixed87.0-1
debian debianbookwormfixed78.9.0esr-1
debian debianbullseyefixed78.9.0esr-1
debian debianforkyfixed78.9.0esr-1
debian debiantrixiefixed78.9.0esr-1

References

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