Description
Mozilla developers and community members reported memory safety bugs present in Firefox 93 and Firefox ESR 91.2. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. 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 20.04 LTS | thunderbird | 1:91.5.0+build1-0ubuntu0.20.04.1 | USN-5248-1 |
| 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 |
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 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.23 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.22 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.21 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.20 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.19 | thunderbird | 91.3.2-r0 | — |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.18 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.17 | thunderbird | 91.3.2-r0 | — |
| Alpine v3.16 | thunderbird | 91.3.2-r0 | — |
Advisories 16
- 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
- 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
- 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
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/buglist.cgi?bug_id=1606864%2C1712671%2C1730048%2C1735152
- 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