Sandbox Escape Vulnerability in Firefox by Mozilla
CVE-2026-100818

9.6CRITICAL

Key Information:

Vendor

Mozilla
Status
Thunderbird
Firefox
Vendor
CVE Published:
29 September 2026

What is CVE-2026-100818?

The vulnerability stems from a use-after-free condition in the Widget: Gtk component, which allows attackers to escape the sandbox and potentially execute arbitrary code within affected Firefox versions. The flaw has been addressed in Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17. Users are encouraged to upgrade their browser to the latest version to safeguard against potential exploitation.

Affected Version(s)

Firefox 140.17

Firefox 153.4

Firefox 157

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2069399
https://www.mozilla.org/security/advisories/mfsa2026-100/
https://www.mozilla.org/security/advisories/mfsa2026-101/

CVSS V3.1

Score:
9.6
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
Required
Scope:
Changed

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Mozilla
.