Vulnerability · Published Sep 29, 2026 · Assigned by mozilla
CVE-2026-100787Sandbox escape in the XUL component
Critical 9.6
In plain English
A critical-severity improper input validation 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 23% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)9.6Critical
Exploit odds (30 days)0.3%top 77.1% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Sandbox escape in the XUL component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 153.4, and Firefox 157.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | firefox-esr | 153.4.0esr-1~deb12u1 | DEBIAN-CVE-2026-100787 |
| Debian:13 | firefox-esr | 153.4.0esr-1~deb13u1 | DEBIAN-CVE-2026-100787 |
| Debian:14 | firefox-esr | 153.4.0esr-1 | DEBIAN-CVE-2026-100787 |
| Debian:14 | thunderbird | 1:153.4.0esr-1 | DEBIAN-CVE-2026-100787 |
| Ubuntu:22.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-100787 |
| Ubuntu:24.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-100787 |
| Ubuntu:24.04:LTS | mozjs115 | no fix listed | UBUNTU-CVE-2026-100787 |
| Ubuntu:22.04:LTS | mozjs78 | no fix listed | UBUNTU-CVE-2026-100787 |
| Ubuntu:22.04:LTS | mozjs91 | no fix listed | UBUNTU-CVE-2026-100787 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-100787 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | see references |
| Mozilla | Thunderbird | see references |
Weakness: CWE-20 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H