Vulnerability · Published Apr 21, 2026 · Assigned by mozilla
CVE-2026-6766Incorrect boundary conditions in the Libraries component in NSS
High 7.5
In plain English
A high-severity security flaw 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 17% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.3%top 82.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Incorrect boundary conditions in the Libraries component in NSS. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | firefox | 140.10.0-1.el10_1 | ALSA-2026:10767 |
| AlmaLinux:8 | firefox | 140.10.0-1.el8_10.alma.1 | ALSA-2026:10766 |
| AlmaLinux:9 | firefox | 140.10.0-1.el9_7.alma.1 | ALSA-2026:10757 |
| AlmaLinux:9 | firefox-x11 | 140.10.0-1.el9_7.alma.1 | ALSA-2026:10757 |
| AlmaLinux:10 | thunderbird | 140.10.0-1.el10_1.alma.1 | ALSA-2026:12285 |
| AlmaLinux:8 | thunderbird | 140.10.0-1.el8_10.alma.1 | ALSA-2026:13537 |
| AlmaLinux:9 | thunderbird | 140.10.0-1.el9_7.alma.1 | ALSA-2026:15892 |
| AlmaLinux:9 | thunderbird | 140.10.1-1.el9_8.alma.1 | ALSA-2026:19348 |
| Debian:12 | firefox-esr | 140.10.0esr-1~deb12u1 | DEBIAN-CVE-2026-6766 |
| Debian:13 | firefox-esr | 140.10.0esr-1~deb13u1 | DEBIAN-CVE-2026-6766 |
| Debian:14 | firefox-esr | 140.10.0esr-1 | DEBIAN-CVE-2026-6766 |
| Debian:12 | nss | 2:3.87.1-1+deb12u3 | DEBIAN-CVE-2026-6766 |
| Debian:13 | nss | 2:3.110-1+deb13u2 | DEBIAN-CVE-2026-6766 |
| Debian:14 | nss | 2:3.123-1 | DEBIAN-CVE-2026-6766 |
| Debian:12 | thunderbird | 1:140.10.0esr-1~deb12u1 | DEBIAN-CVE-2026-6766 |
| Debian:13 | thunderbird | 1:140.10.0esr-1~deb13u1 | DEBIAN-CVE-2026-6766 |
| Debian:14 | thunderbird | 1:140.10.0esr-1 | DEBIAN-CVE-2026-6766 |
| Rocky Linux:10 | firefox | 0:140.10.0-1.el10_1 | RLSA-2026:10767 |
| Rocky Linux:8 | firefox | 0:140.10.0-1.el8_10 | RLSA-2026:10766 |
| Rocky Linux:9 | firefox | 0:140.10.0-1.el9_7 | RLSA-2026:10757 |
| Rocky Linux:9 | firefox | 0:140.10.0-1.el9_7 | RLSA-2026:19201 |
| Rocky Linux:10 | thunderbird | 0:140.10.0-1.el10_1 | RLSA-2026:12285 |
| Rocky Linux:8 | thunderbird | 0:140.10.0-1.el8_10 | RLSA-2026:13537 |
| Rocky Linux:9 | thunderbird | 0:140.10.1-1.el9_8 | RLSA-2026:19348 |
| Rocky Linux:9 | thunderbird | 0:140.10.0-1.el9_7 | RLSA-2026:15892 |
| Ubuntu:22.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-6766 |
| Ubuntu:24.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-6766 |
| Ubuntu:24.04:LTS | mozjs115 | no fix listed | UBUNTU-CVE-2026-6766 |
| Ubuntu:22.04:LTS | mozjs78 | no fix listed | UBUNTU-CVE-2026-6766 |
| Ubuntu:22.04:LTS | mozjs91 | no fix listed | UBUNTU-CVE-2026-6766 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-6766 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | see references |
| Mozilla | Thunderbird | see references |
Weakness: CWE-754 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N