Description
A use-after-free could have occured when an HTTP2 session object was released on a different thread, leading to memory corruption and a potentially exploitable crash. This vulnerability affects Firefox < 93, Thunderbird < 91.3, and Firefox ESR < 91.3.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mozilla | Firefox | unspecified – < 93 | 93 |
| 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 15
- 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
References
- https://www.mozilla.org/security/advisories/mfsa2021-43/
- https://www.mozilla.org/security/advisories/mfsa2021-49/
- https://www.mozilla.org/security/advisories/mfsa2021-50/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1667102
- 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