Vulnerability · Published Aug 18, 2026 · Assigned by mozilla
CVE-2026-74987Internally found bugs fixed in Firefox ESR 140.14, Firefox ESR 153.1 and Firefox 154
Critical 9.8
In plain English
A critical-severity memory corruption 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 0.7% (higher than 54% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Internally found bugs present in Firefox ESR 140.13, Firefox ESR 153.0 and Firefox 153. 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 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | firefox | 140.14.0-1.el10_2 | ALSA-2026:58899 |
| AlmaLinux:8 | firefox | 140.14.0-1.el8_10.alma.1 | ALSA-2026:58898 |
| AlmaLinux:9 | firefox | 140.14.0-1.el9_8.alma.1 | ALSA-2026:58897 |
| AlmaLinux:9 | firefox-x11 | 140.14.0-1.el9_8.alma.1 | ALSA-2026:58897 |
| AlmaLinux:10 | thunderbird | 140.14.0-1.el10_2.alma.1 | ALSA-2026:65159 |
| AlmaLinux:8 | thunderbird | 140.14.0-1.el8_10.alma.1 | ALSA-2026:65160 |
| AlmaLinux:9 | thunderbird | 140.14.0-1.el9_8.alma.1 | ALSA-2026:65158 |
| Debian:12 | firefox-esr | 140.14.0esr-1~deb12u1 | DEBIAN-CVE-2026-74987 |
| Debian:13 | firefox-esr | 140.14.0esr-1~deb13u1 | DEBIAN-CVE-2026-74987 |
| Debian:14 | firefox-esr | 140.14.0esr-2 | DEBIAN-CVE-2026-74987 |
| Debian:12 | thunderbird | 1:140.14.0esr-1~deb12u1 | DEBIAN-CVE-2026-74987 |
| Debian:13 | thunderbird | 1:140.14.0esr-1~deb13u1 | DEBIAN-CVE-2026-74987 |
| Debian:14 | thunderbird | 1:140.14.0esr-1 | DEBIAN-CVE-2026-74987 |
| Rocky Linux:10 | firefox | 0:140.14.0-1.el10_2 | RLSA-2026:58899 |
| Rocky Linux:8 | firefox | 0:140.14.0-1.el8_10 | RLSA-2026:58898 |
| Rocky Linux:9 | firefox | 0:140.14.0-1.el9_8 | RLSA-2026:58897 |
| Rocky Linux:10 | thunderbird | 0:140.14.0-1.el10_2 | RLSA-2026:65159 |
| Rocky Linux:8 | thunderbird | 0:140.14.0-1.el8_10 | RLSA-2026:65160 |
| Rocky Linux:9 | thunderbird | 0:140.14.0-1.el9_8 | RLSA-2026:65158 |
| Ubuntu:22.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-74987 |
| Ubuntu:24.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-74987 |
| Ubuntu:24.04:LTS | mozjs115 | no fix listed | UBUNTU-CVE-2026-74987 |
| Ubuntu:22.04:LTS | mozjs78 | no fix listed | UBUNTU-CVE-2026-74987 |
| Ubuntu:22.04:LTS | mozjs91 | no fix listed | UBUNTU-CVE-2026-74987 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-74987 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | see references |
| Mozilla | Thunderbird | see references |
Weakness: CWE-119 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- Moderate Severity internally found bugs fixed in Firefox ESR 140.14, Firefox ESR 153.1 and Firefox 154
- High Severity internally found bugs fixed in Firefox ESR 140.14, Firefox ESR 153.1 and Firefox 154
- Low Severity internally found bugs fixed in Firefox ESR 140.14, Firefox ESR 153.1 and Firefox 154
- https://www.mozilla.org/security/advisories/mfsa2026-74/
- https://www.mozilla.org/security/advisories/mfsa2026-76/
- https://www.mozilla.org/security/advisories/mfsa2026-77/
- https://www.mozilla.org/security/advisories/mfsa2026-78/
- https://www.mozilla.org/security/advisories/mfsa2026-79/
- https://www.mozilla.org/security/advisories/mfsa2026-80/