Vulnerability · Published Aug 18, 2026 · Assigned by mozilla
CVE-2026-74960Site isolation issue in the WebExtensions component
High 8.1
In plain English
A high-severity improper access control 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 0.2% (higher than 13% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)8.1High
Exploit odds (30 days)0.2%top 86.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Site isolation issue in the WebExtensions component. 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-2026-74960 |
| Debian:13 | firefox-esr | 140.14.0esr-1~deb13u1 | DEBIAN-CVE-2026-74960 |
| Debian:14 | firefox-esr | 140.14.0esr-2 | DEBIAN-CVE-2026-74960 |
| Debian:12 | thunderbird | 1:140.14.0esr-1~deb12u1 | DEBIAN-CVE-2026-74960 |
| Debian:13 | thunderbird | 1:140.14.0esr-1~deb13u1 | DEBIAN-CVE-2026-74960 |
| Debian:14 | thunderbird | 1:140.14.0esr-1 | DEBIAN-CVE-2026-74960 |
| 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-2026-74960 |
| Ubuntu:24.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-74960 |
| Ubuntu:24.04:LTS | mozjs115 | no fix listed | UBUNTU-CVE-2026-74960 |
| Ubuntu:22.04:LTS | mozjs78 | no fix listed | UBUNTU-CVE-2026-74960 |
| Ubuntu:22.04:LTS | mozjs91 | no fix listed | UBUNTU-CVE-2026-74960 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-74960 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | see references |
| Mozilla | Thunderbird | see references |
Weakness: CWE-346, CWE-284 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2049148
- 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/