Description
Through a series of navigations, Firefox could have entered fullscreen mode without notification or warning to the user. This could lead to spoofing attacks on the browser UI including phishing. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mozilla | Firefox | unspecified – < 94 | 94 |
| Mozilla | Thunderbird | unspecified – < 91.3 | 91.3 |
| Mozilla | Firefox ESR | unspecified – < 91.3 | 91.3 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | firefox-esr | 91.3.0esr-1 | — |
| Debian 14 | thunderbird | 1:91.3.0-1 | — |
| Debian 13 | firefox-esr | 91.3.0esr-1 | — |
| Debian 13 | thunderbird | 1:91.3.0-1 | — |
| Debian 12 | firefox-esr | 91.3.0esr-1 | — |
| Debian 12 | thunderbird | 1:91.3.0-1 | — |
| Debian 11 | firefox-esr | 91.4.1esr-1~deb11u1 | DSA-5026-1 |
| Debian 11 | thunderbird | 1:91.4.1-1~deb11u1 | DSA-5034-1 |
| Debian 10 | thunderbird | 1:91.4.1-1~deb10u1 | DSA-5034-1 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 9 | firefox-esr | 91.4.1esr-1~deb9u1 | DLA-2863-1 |
| Debian 9 | thunderbird | 1:91.4.1-1~deb9u1 | DLA-2874-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 22.04 LTS | firefox | 94.0+build3-0ubuntu1 | — |
| Ubuntu 22.04 LTS | mozjs78 | No fix yet | — |
| Ubuntu 22.04 LTS | thunderbird | 1:91.3.1+build1-0ubuntu1 | — |
| Ubuntu 20.04 LTS | firefox | 94.0+build3-0ubuntu0.20.04.1 | USN-5131-1 |
| Ubuntu 20.04 LTS | mozjs52 +1 | No fix yet | — |
| Ubuntu 20.04 LTS | thunderbird | 1:91.5.0+build1-0ubuntu0.20.04.1 | USN-5248-1 |
| Ubuntu 18.04 LTS | firefox | 94.0+build3-0ubuntu0.18.04.1 | USN-5131-1 |
| Ubuntu 18.04 LTS | mozjs38 +1 | No fix yet | — |
| Ubuntu 18.04 LTS | thunderbird | 1:91.5.0+build1-0ubuntu0.18.04.1 | USN-5248-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 8 | firefox | 91.3.0-1.el8_4 | RHSA-2021:4123 |
| RHEL 8 | thunderbird | 91.3.0-2.el8_4 | RHSA-2021:4130 |
| RHEL 7 | firefox | 91.3.0-1.el7_9 | RHSA-2021:4116 |
| RHEL 7 | thunderbird | 91.3.0-2.el7_9 | RHSA-2021:4134 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 8.2 EUS | firefox | 91.3.0-1.el8_2 | RHSA-2021:4605 |
| RHEL 8.2 EUS | thunderbird | 91.3.0-2.el8_2 | RHSA-2021:4132 |
| RHEL 8.1 EUS | firefox | 91.3.0-1.el8_1 | RHSA-2021:4607 |
| RHEL 8.1 EUS | thunderbird | 91.3.0-2.el8_1 | RHSA-2021:4133 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 8 | firefox | 91.3.0-1.el8_4.alma | ALSA-2021:4123 |
| AlmaLinux 8 | thunderbird | 91.3.0-2.el8_4.alma | ALSA-2021:4130 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 8 | firefox | 91.3.0-1.el8 | RLSA-2021:4123 |
| Rocky Linux 8 | thunderbird | 91.3.0-2.el8 | RLSA-2021:4130 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP3 | MozillaFirefox | 91.3.0-152.6.1 | SUSE-SU-2021:3745-1 |
| SLES 15 SP3 | MozillaThunderbird | 91.4.0-8.45.2 | SUSE-SU-2021:4150-1 |
| SLES 15 SP2 | MozillaFirefox | 91.3.0-152.6.1 | SUSE-SU-2021:3745-1 |
| SLES 15 SP2 | MozillaThunderbird | 91.4.0-8.45.2 | SUSE-SU-2021:4150-1 |
| SLES 15 SP1 | MozillaFirefox | 91.3.0-150.6.1 | SUSE-SU-2021:3651-1 |
| SLES 15 | MozillaFirefox | 91.3.0-150.6.1 | SUSE-SU-2021:3651-1 |
| SLES 12 SP5 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
Show 16 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 12 SP4 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SLES 12 SP3 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SLES 12 SP2 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SLES for SAP 15 SP1 | MozillaFirefox | 91.3.0-150.6.1 | SUSE-SU-2021:3651-1 |
| SLES for SAP 15 | MozillaFirefox | 91.3.0-150.6.1 | SUSE-SU-2021:3651-1 |
| SLES for SAP 12 SP5 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SLES for SAP 12 SP4 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SLES for SAP 12 SP3 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SLE HPC 15 SP1 | MozillaFirefox | 91.3.0-150.6.1 | SUSE-SU-2021:3651-1 |
| SLE HPC 15 | MozillaFirefox | 91.3.0-150.6.1 | SUSE-SU-2021:3651-1 |
| SUSE OpenStack Cloud Crowbar 9 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SUSE OpenStack Cloud Crowbar 8 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SUSE OpenStack Cloud 9 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SUSE OpenStack Cloud 8 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SUSE HPE Helion OpenStack 8 | MozillaFirefox | 91.3.0-112.80.2 | SUSE-SU-2021:3721-1 |
| SUSE Enterprise Storage 6 | MozillaFirefox | 91.3.0-150.6.1 | SUSE-SU-2021:3651-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | MozillaFirefox | 94.0.1-1.1 | openSUSE-SU-2024:11614-1 |
| openSUSE Tumbleweed | MozillaThunderbird | 91.3.0-1.1 | openSUSE-SU-2024:11607-1 |
| openSUSE Tumbleweed | firefox-esr | 128.5.1-1.1 | openSUSE-SU-2024:14572-1 |
| openSUSE Leap 15.3 | MozillaFirefox | 91.3.0-152.6.1 | openSUSE-SU-2021:3745-1 |
| openSUSE Leap 15.3 | MozillaThunderbird | 91.4.0-8.45.2 | openSUSE-SU-2021:4150-1 |
| openSUSE Leap 15.2 | MozillaThunderbird | 91.4.0-lp152.2.52.1 | openSUSE-SU-2021:1635-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | librewolf | 94.0-r0 | — |
| Alpine v3.23 | firefox +1 | 94.0-r0 | — |
| Alpine v3.23 | firefox-esr | 91.3.0-r0 | — |
| Alpine v3.23 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.22 | firefox +1 | 94.0-r0 | — |
| Alpine v3.22 | firefox-esr | 91.3.0-r0 | — |
| Alpine v3.22 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.21 | firefox +1 | 94.0-r0 | — |
| Alpine v3.21 | firefox-esr | 91.3.0-r0 | — |
| Alpine v3.21 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.20 | firefox | 94.0-r0 | — |
| Alpine v3.20 | firefox-esr | 91.3.0-r0 | — |
| Alpine v3.20 | thunderbird | 91.3.2-r0 | — |
Show 5 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | firefox | 94.0-r0 | — |
| Alpine v3.19 | firefox-esr | 91.3.0-r0 | — |
| Alpine v3.19 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.18 | firefox | 94.0-r0 | — |
| Alpine v3.18 | firefox-esr | 91.3.0-r0 | — |
| Alpine v3.18 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.17 | firefox | 94.0-r0 | — |
| Alpine v3.17 | firefox-esr | 91.3.0-r0 | — |
| Alpine v3.17 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.16 | firefox | 94.0-r0 | — |
| Alpine v3.16 | firefox-esr | 91.3.0-r0 | — |
| Alpine v3.16 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.15 | firefox | 94.0-r0 | — |
| Alpine v3.15 | firefox-esr | 91.3.0-r0 | — |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 8 | firefox | 91.3.0-1.0.1.el8_4 | ELSA-2021-4123 |
| Oracle Linux 8 | thunderbird | 91.3.0-2.0.1.el8_4 | ELSA-2021-4130 |
| Oracle Linux 7 | firefox | 91.3.0-1.0.1.el7_9 | ELSA-2021-4116 |
| Oracle Linux 7 | thunderbird | 91.3.0-2.0.1.el7_9 | ELSA-2021-4134 |
Advisories 33
- ALSA-2021:4123 Important: firefox security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2021:4130 Important: thunderbird security update AlmaLinux Security Advisories · Oct 29, 2026
- RHSA-2021:4134 Red Hat Security Advisory: thunderbird security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- RHSA-2021:4116 Red Hat Security Advisory: firefox security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- USN-5248-1 thunderbird vulnerabilities Ubuntu Security Notices (USN) · Apr 27, 2026
- USN-5131-1 firefox vulnerabilities Ubuntu Security Notices (USN) · Apr 22, 2026
- DSA-5034-1 thunderbird - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DSA-5026-1 firefox-esr - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-2863-1 firefox-esr - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-2874-1 thunderbird - security update Debian Security (DSA / DLA) · Mar 9, 2026
- RLSA-2021:4123 Important: firefox security update Rocky Linux Security Advisories · Feb 4, 2026
- RLSA-2021:4130 Important: thunderbird security update Rocky Linux Security Advisories · Feb 4, 2026
- SUSE-SU-2021:4150-1 Security update for MozillaThunderbird SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:3651-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2021:4150-1 Security update for MozillaThunderbird SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2024:11607-1 MozillaThunderbird-91.3.0-1.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2021:1635-1 Security update for MozillaThunderbird SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:3721-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2021:3745-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:3745-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2024:14572-1 firefox-esr-128.5.1-1.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- RHSA-2021:4607 Red Hat Security Advisory: firefox security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:4605 Red Hat Security Advisory: firefox security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:4133 Red Hat Security Advisory: thunderbird security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:4132 Red Hat Security Advisory: thunderbird security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:4123 Red Hat Security Advisory: firefox security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:4130 Red Hat Security Advisory: thunderbird security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- WID-SEC-2023-0839 Xerox FreeFlow Print Server: Mehrere Schwachstellen BSI CERT-Bund (WID) · Oct 6, 2025
- openSUSE-SU-2024:11614-1 MozillaFirefox-94.0.1-1.1 on GA media SUSE / openSUSE Security Updates · May 7, 2025
- ELSA-2021-4134 Important: thunderbird security update (Oracle Linux 7) Oracle Linux Security Advisories (ELSA) · Nov 5, 2021
- ELSA-2021-4130 Important: thunderbird security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Nov 5, 2021
- ELSA-2021-4116 Important: firefox security update (Oracle Linux 7) Oracle Linux Security Advisories (ELSA) · Nov 4, 2021
- ELSA-2021-4123 Important: firefox security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Nov 4, 2021
References
- https://www.mozilla.org/security/advisories/mfsa2021-49/
- https://www.mozilla.org/security/advisories/mfsa2021-50/
- https://www.mozilla.org/security/advisories/mfsa2021-48/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1730750
- DSA-5026 vendor-advisory
- [debian-lts-announce] 20211229 [SECURITY] [DLA 2863-1] firefox-esr security update mailing-list
- DSA-5034 vendor-advisory
- [debian-lts-announce] 20220104 [SECURITY] [DLA 2874-1] thunderbird security update mailing-list
- GLSA-202202-03 vendor-advisory
- GLSA-202208-14 vendor-advisory