Vulnerability · Published Sep 1, 2026 · Assigned by mozilla
CVE-2026-84143Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15
Critical 9.8
In plain English
A critical-severity information exposure in Firefox from Mozilla. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 32% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | firefox | 140.15.0-1.el10_2 | ALSA-2026:67129 |
| AlmaLinux:8 | firefox | 140.15.0-1.el8_10.alma.1 | ALSA-2026:68549 |
| AlmaLinux:9 | firefox | 140.15.0-1.el9_8.alma.1 | ALSA-2026:67133 |
| AlmaLinux:9 | firefox-x11 | 140.15.0-1.el9_8.alma.1 | ALSA-2026:67133 |
| AlmaLinux:10 | thunderbird | 140.16.0-1.el10_2.alma.1 | ALSA-2026:73130 |
| AlmaLinux:8 | thunderbird | 140.16.0-1.el8_10.alma.1 | ALSA-2026:73971 |
| AlmaLinux:9 | thunderbird | 140.16.0-1.el9_8.alma.1 | ALSA-2026:70642 |
| Debian:12 | firefox-esr | 140.15.0esr-1~deb12u1 | DEBIAN-CVE-2026-84143 |
| Debian:13 | firefox-esr | 140.15.0esr-1~deb13u1 | DEBIAN-CVE-2026-84143 |
| Debian:14 | firefox-esr | 140.15.0esr-1 | DEBIAN-CVE-2026-84143 |
| Debian:12 | thunderbird | 1:140.15.0esr-1~deb12u1 | DEBIAN-CVE-2026-84143 |
| Debian:13 | thunderbird | 1:140.15.0esr-1~deb13u1 | DEBIAN-CVE-2026-84143 |
| Debian:14 | thunderbird | 1:153.2.0esr-1 | DEBIAN-CVE-2026-84143 |
| Rocky Linux:10 | firefox | 0:140.15.0-1.el10_2 | RLSA-2026:67129 |
| Rocky Linux:8 | firefox | 0:140.15.0-1.el8_10 | RLSA-2026:68549 |
| Rocky Linux:9 | firefox | 0:140.15.0-1.el9_8 | RLSA-2026:67133 |
| Rocky Linux:10 | thunderbird | 0:140.16.0-1.el10_2 | RLSA-2026:73130 |
| Rocky Linux:8 | thunderbird | 0:140.16.0-1.el8_10 | RLSA-2026:73971 |
| Rocky Linux:9 | thunderbird | 0:140.16.0-1.el9_8 | RLSA-2026:70642 |
| Ubuntu:22.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-84143 |
| Ubuntu:24.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-84143 |
| Ubuntu:24.04:LTS | mozjs115 | no fix listed | UBUNTU-CVE-2026-84143 |
| Ubuntu:22.04:LTS | mozjs78 | no fix listed | UBUNTU-CVE-2026-84143 |
| Ubuntu:22.04:LTS | mozjs91 | no fix listed | UBUNTU-CVE-2026-84143 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-84143 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | see references |
| Mozilla | Thunderbird | see references |
Weakness: CWE-200 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- High Severity internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15
- Moderate Severity internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15
- Low Severity internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15
- https://www.mozilla.org/security/advisories/mfsa2026-82/
- https://www.mozilla.org/security/advisories/mfsa2026-84/
- https://www.mozilla.org/security/advisories/mfsa2026-85/
- https://www.mozilla.org/security/advisories/mfsa2026-86/
- https://www.mozilla.org/security/advisories/mfsa2026-87/
- https://www.mozilla.org/security/advisories/mfsa2026-88/