CVE-2026-100818 Firefox - Sandbox Escape

Firefox ESR < 153.4, Firefox < 157, and Firefox ESR < 140.17 contain a sandbox escape caused by use-after-free in the Widget: Gtk component, letting attackers escape sandbox restrictions, exploit requires crafted input.

CVSS base score 9.6 /10
Critical
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.26% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Sandbox Escape
Impact
Privilege Escalation
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Published
29 September 2026
Updated
15 October 2026
Weakness
CWE-416

Vendor fix

Update to Firefox ESR 153.4, Firefox 157, or Firefox ESR 140.17 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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