Vulnerability · Published Oct 13, 2026 · Assigned by mozilla
CVE-2026-109778Privilege escalation in the WebExtensions component
High 8.8
In plain English
A high-severity privilege mismanagement 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)8.8High
Exploit odds (30 days)0.3%top 79.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Privilege escalation in the WebExtensions component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | firefox-esr | 153.5.0esr-1~deb12u1 | DEBIAN-CVE-2026-109778 |
| Debian:13 | firefox-esr | 153.5.0esr-1~deb13u1 | DEBIAN-CVE-2026-109778 |
| Debian:14 | firefox-esr | 153.5.0esr-1 | DEBIAN-CVE-2026-109778 |
| Debian:12 | thunderbird | 1:153.5.1esr-1~deb12u1 | DEBIAN-CVE-2026-109778 |
| Debian:13 | thunderbird | 1:153.5.1esr-1~deb13u1 | DEBIAN-CVE-2026-109778 |
| Debian:14 | thunderbird | 1:153.5.0esr-1 | DEBIAN-CVE-2026-109778 |
| Ubuntu:22.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-109778 |
| Ubuntu:24.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-109778 |
| Ubuntu:24.04:LTS | mozjs115 | no fix listed | UBUNTU-CVE-2026-109778 |
| Ubuntu:22.04:LTS | mozjs78 | no fix listed | UBUNTU-CVE-2026-109778 |
| Ubuntu:22.04:LTS | mozjs91 | no fix listed | UBUNTU-CVE-2026-109778 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-109778 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | see references |
| Mozilla | Thunderbird | see references |
Weakness: CWE-269 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H