Description
Mozilla developers and community members reported memory safety bugs present in Firefox 86 and Firefox ESR 78.8. 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 ESR < 78.9, Firefox < 87, and Thunderbird < 78.9.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mozilla | Firefox ESR | unspecified – < 78.9 | 78.9 |
| Mozilla | Firefox | unspecified – < 87 | 87 |
| Mozilla | Thunderbird | unspecified – < 78.9 | 78.9 |
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 | 78.9.0esr-1 | — |
| Debian 14 | thunderbird | 1:78.9.0-1 | — |
| Debian 13 | firefox-esr | 78.9.0esr-1 | — |
| Debian 13 | thunderbird | 1:78.9.0-1 | — |
| Debian 12 | firefox-esr | 78.9.0esr-1 | — |
| Debian 12 | thunderbird | 1:78.9.0-1 | — |
| Debian 10 | firefox-esr | 78.9.0esr-1~deb10u1 | DSA-4874-1 |
| Debian 10 | thunderbird | 1:78.9.0-1~deb10u1 | DSA-4876-1 |
| Debian 9 | firefox-esr | 78.9.0esr-1~deb9u1 | DLA-2607-1 |
| Debian 9 | thunderbird | 1:78.9.0-1~deb9u1 | DLA-2609-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 22.04 LTS | mozjs78 | No fix yet | — |
| Ubuntu 20.04 LTS | firefox | 87.0+build3-0ubuntu0.20.04.2 | USN-4893-1 |
| Ubuntu 20.04 LTS | mozjs52 +1 | No fix yet | — |
| Ubuntu 20.04 LTS | thunderbird | 1:78.11.0+build1-0ubuntu0.20.04.2 | USN-4995-1 |
| Ubuntu 18.04 LTS | firefox | 87.0+build3-0ubuntu0.18.04.2 | USN-4893-1 |
| Ubuntu 18.04 LTS | mozjs38 +1 | No fix yet | — |
| Ubuntu 18.04 LTS | thunderbird | 1:78.11.0+build1-0ubuntu0.18.04.2 | USN-4995-2 |
| Ubuntu 16.04 LTS | firefox | 87.0+build3-0ubuntu0.16.04.2 | USN-4893-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 8 | firefox | 78.9.0-1.el8_3 | RHSA-2021:0990 |
| RHEL 8 | thunderbird | 78.9.0-3.el8_3 | RHSA-2021:0993 |
| RHEL 7 | firefox | 78.9.0-1.el7_9 | RHSA-2021:0992 |
| RHEL 7 | thunderbird | 78.9.0-3.el7_9 | RHSA-2021:0996 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 8.2 EUS | firefox | 78.9.0-1.el8_2 | RHSA-2021:0989 |
| RHEL 8.2 EUS | thunderbird | 78.9.0-3.el8_2 | RHSA-2021:0994 |
| RHEL 8.1 EUS | firefox | 78.9.0-1.el8_1 | RHSA-2021:0991 |
| RHEL 8.1 EUS | thunderbird | 78.9.0-3.el8_1 | RHSA-2021:0995 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP2 | MozillaFirefox | 78.9.0-8.35.1 | SUSE-SU-2021:0966-1 |
| SLES 15 SP2 | MozillaThunderbird | 78.9.1-8.20.1 | SUSE-SU-2021:1167-1 |
| SLES 15 SP2 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SLES 15 SP1 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SLES 15 SP1 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SLES 15 SP1 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SLES 15 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SLES 15 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SLES 15 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SLES 12 SP5 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SLES 12 SP4 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
Show 22 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 12 SP3 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SLES 12 SP2 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SLES 11 SP4 | MozillaFirefox | 78.9.0-78.123.1 | SUSE-SU-2021:14684-1 |
| SLES for SAP 15 SP1 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SLES for SAP 15 SP1 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SLES for SAP 15 SP1 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SLES for SAP 15 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SLES for SAP 15 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SLES for SAP 15 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SLES for SAP 12 SP5 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SLES for SAP 12 SP4 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SLES for SAP 12 SP3 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SLES for SAP 12 SP2 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SLE Micro 5.0 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SLE HPC 15 SP1 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SLE HPC 15 SP1 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SLE HPC 15 SP1 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SLE HPC 15 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SLE HPC 15 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SLE HPC 15 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SUSE OpenStack Cloud Crowbar 9 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SUSE OpenStack Cloud Crowbar 8 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SUSE OpenStack Cloud 9 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SUSE OpenStack Cloud 8 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SUSE OpenStack Cloud 7 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SUSE Manager Server 4.0 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SUSE Manager Server 4.0 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SUSE Manager Server 4.0 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SUSE Manager Retail Branch Server 4.0 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SUSE Manager Retail Branch Server 4.0 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SUSE Manager Retail Branch Server 4.0 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SUSE Manager Proxy 4.0 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SUSE Manager Proxy 4.0 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SUSE Manager Proxy 4.0 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
| SUSE HPE Helion OpenStack 8 | MozillaFirefox | 78.9.0-112.54.1 | SUSE-SU-2021:0999-1 |
| SUSE Enterprise Storage 6 | MozillaFirefox | 78.9.0-3.136.1 | SUSE-SU-2021:1007-1 |
| SUSE Enterprise Storage 6 | MozillaFirefox-branding-SLE | 78-4.16.1 | SUSE-SU-2021:1007-1 |
| SUSE Enterprise Storage 6 | mozilla-nspr | 4.25.1-3.17.1 | SUSE-SU-2021:1007-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | MozillaFirefox | 92.0-1.2 | openSUSE-SU-2024:10600-1 |
| openSUSE Tumbleweed | MozillaThunderbird | 91.1.1-1.1 | openSUSE-SU-2024:10601-1 |
| openSUSE Tumbleweed | firefox-esr | 128.5.1-1.1 | openSUSE-SU-2024:14572-1 |
| openSUSE Leap 15.2 | MozillaFirefox | 78.9.0-lp152.2.52.1 | openSUSE-SU-2021:0487-1 |
| openSUSE Leap 15.2 | MozillaThunderbird | 78.9.1-lp152.2.38.1 | openSUSE-SU-2021:0580-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | librewolf | 87.0-r0 | — |
| Alpine v3.23 | firefox +1 | 87.0-r0 | — |
| Alpine v3.23 | firefox-esr +1 | 78.9.0-r0 | — |
| Alpine v3.22 | firefox +1 | 87.0-r0 | — |
| Alpine v3.22 | firefox-esr +1 | 78.9.0-r0 | — |
| Alpine v3.21 | firefox +1 | 87.0-r0 | — |
| Alpine v3.21 | firefox-esr +1 | 78.9.0-r0 | — |
| Alpine v3.20 | firefox | 87.0-r0 | — |
| Alpine v3.20 | firefox-esr +1 | 78.9.0-r0 | — |
Show 8 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | firefox | 87.0-r0 | — |
| Alpine v3.19 | firefox-esr +1 | 78.9.0-r0 | — |
| Alpine v3.18 | firefox | 87.0-r0 | — |
| Alpine v3.18 | firefox-esr +1 | 78.9.0-r0 | — |
| Alpine v3.17 | firefox | 87.0-r0 | — |
| Alpine v3.17 | firefox-esr +1 | 78.9.0-r0 | — |
| Alpine v3.16 | firefox | 87.0-r0 | — |
| Alpine v3.16 | mozjs78 +2 | 78.9.0-r0 | — |
| Alpine v3.15 | firefox | 87.0-r0 | — |
| Alpine v3.15 | mozjs78 +1 | 78.9.0-r0 | — |
| Alpine v3.14 | firefox | 87.0-r0 | — |
| Alpine v3.14 | mozjs78 +1 | 78.9.0-r0 | — |
| Alpine v3.13 | firefox | 87.0-r0 | — |
| Alpine v3.13 | mozjs78 +1 | 78.9.0-r0 | — |
| Alpine v3.12 | firefox-esr | 78.9.0-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2 | thunderbird | 78.9.0-3.amzn2 | ALAS2-2021-1632 |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 8 | firefox | 78.9.0-1.0.1.el8_3 | ELSA-2021-0990 |
| Oracle Linux 8 | thunderbird | 78.9.0-3.0.1.el8_3 | ELSA-2021-0993 |
| Oracle Linux 7 | firefox | 78.9.0-1.0.1.el7_9 | ELSA-2021-0992 |
| Oracle Linux 7 | thunderbird | 78.9.0-3.0.1.el7_9 | ELSA-2021-0996 |
Advisories 30
- RHSA-2021:0992 Red Hat Security Advisory: firefox security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- RHSA-2021:0996 Red Hat Security Advisory: thunderbird security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- USN-4995-2 thunderbird vulnerabilities Ubuntu Security Notices (USN) · Apr 22, 2026
- USN-4995-1 thunderbird vulnerabilities Ubuntu Security Notices (USN) · Apr 22, 2026
- USN-4893-1 firefox vulnerabilities Ubuntu Security Notices (USN) · Apr 22, 2026
- DSA-4876-1 thunderbird - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DSA-4874-1 firefox-esr - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-2607-1 firefox-esr - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-2609-1 thunderbird - security update Debian Security (DSA / DLA) · Mar 9, 2026
- openSUSE-SU-2021:0487-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:1167-1 Security update for MozillaThunderbird SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:0999-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2024:10600-1 MozillaFirefox-92.0-1.2 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2021:0580-1 Security update for MozillaThunderbird SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:14684-1 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
- SUSE-SU-2021:0966-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Feb 4, 2026
- RHSA-2021:0995 Red Hat Security Advisory: thunderbird security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:0994 Red Hat Security Advisory: thunderbird security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:0993 Red Hat Security Advisory: thunderbird security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:0991 Red Hat Security Advisory: firefox security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:0989 Red Hat Security Advisory: firefox security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- RHSA-2021:0990 Red Hat Security Advisory: firefox security update Red Hat Security Advisories (RHSA) · Nov 22, 2025
- openSUSE-SU-2024:10601-1 MozillaThunderbird-91.1.1-1.1 on GA media SUSE / openSUSE Security Updates · May 7, 2025
- SUSE-SU-2021:1007-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · May 2, 2025
- ALAS2-2021-1632 Important: thunderbird security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Apr 21, 2021
- ELSA-2021-0990 Important: firefox security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Mar 26, 2021
- ELSA-2021-0993 Important: thunderbird security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Mar 26, 2021
- ELSA-2021-0996 Important: thunderbird security update (Oracle Linux 7) Oracle Linux Security Advisories (ELSA) · Mar 26, 2021
- ELSA-2021-0992 Important: firefox security update (Oracle Linux 7) Oracle Linux Security Advisories (ELSA) · Mar 25, 2021