Vulnerability · Published Jul 21, 2026 · Assigned by mozilla
CVE-2026-16387Site isolation issue in the Networking component
Critical 9.8
In plain English
A critical-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 0.3% (higher than 21% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)9.8Critical
Exploit odds (30 days)0.3%top 79.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Site isolation issue in the Networking component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | firefox | 140.13.0-1.el10_2 | ALSA-2026:47101 |
| AlmaLinux:8 | firefox | 140.13.0-1.el8_10.alma.1 | ALSA-2026:47105 |
| AlmaLinux:9 | firefox | 140.13.0-1.el9_8.alma.1 | ALSA-2026:47104 |
| AlmaLinux:9 | firefox-x11 | 140.13.0-1.el9_8.alma.1 | ALSA-2026:47104 |
| AlmaLinux:10 | thunderbird | 140.13.0-1.el10_2.alma.1 | ALSA-2026:49621 |
| AlmaLinux:8 | thunderbird | 140.13.0-1.el8_10.alma.1 | ALSA-2026:49922 |
| AlmaLinux:9 | thunderbird | 140.13.0-1.el9_8.alma.1 | ALSA-2026:49921 |
| Debian:12 | firefox-esr | 140.13.0esr-1~deb12u1 | DEBIAN-CVE-2026-16387 |
| Debian:13 | firefox-esr | 140.13.0esr-1~deb13u1 | DEBIAN-CVE-2026-16387 |
| Debian:14 | firefox-esr | 140.13.0esr-1 | DEBIAN-CVE-2026-16387 |
| Debian:12 | thunderbird | 1:140.13.0esr-2~deb12u1 | DEBIAN-CVE-2026-16387 |
| Debian:13 | thunderbird | 1:140.13.0esr-2~deb13u1 | DEBIAN-CVE-2026-16387 |
| Debian:14 | thunderbird | 1:140.13.0esr-1 | DEBIAN-CVE-2026-16387 |
| Rocky Linux:10 | firefox | 0:140.13.0-1.el10_2 | RLSA-2026:47101 |
| Rocky Linux:8 | firefox | 0:140.13.0-1.el8_10 | RLSA-2026:47105 |
| Rocky Linux:9 | firefox | 0:140.13.0-1.el9_8 | RLSA-2026:47104 |
| Rocky Linux:10 | thunderbird | 0:140.13.0-1.el10_2 | RLSA-2026:49621 |
| Rocky Linux:8 | thunderbird | 0:140.13.0-1.el8_10 | RLSA-2026:49922 |
| Rocky Linux:9 | thunderbird | 0:140.13.0-1.el9_8 | RLSA-2026:49921 |
| Ubuntu:22.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-16387 |
| Ubuntu:24.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-16387 |
| Ubuntu:24.04:LTS | mozjs115 | no fix listed | UBUNTU-CVE-2026-16387 |
| Ubuntu:22.04:LTS | mozjs78 | no fix listed | UBUNTU-CVE-2026-16387 |
| Ubuntu:22.04:LTS | mozjs91 | no fix listed | UBUNTU-CVE-2026-16387 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-16387 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | see references |
| Mozilla | Thunderbird | see references |
Weakness: CWE-346, CWE-284, CWE-200 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H