CVE-2026-109705 Mozilla Firefox - Use After Free

Mozilla Firefox < 158 and Firefox ESR < 153.5 contain a use-after-free vulnerability caused by incorrect boundary conditions in the Networking component, letting attackers escape sandbox and bypass site isolation, exploit requires crafted network activity.

CVSS base score 9.6 /10
Critical
CISA KEV
Not listed
Public exploit
None known
EPSS
0.31% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Use After Free
Impact
Remote Code Execution, Privilege Escalation
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Published
13 October 2026
Updated
15 October 2026
Weakness
CWE-416

Vendor fix

Update to Firefox 158 or Firefox ESR 153.5 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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