Critical 9.6Published Oct 13, 2026

CVE-2026-109705Sandbox escape, site isolation issue due to incorrect boundary conditions, use-after-free in the Networking component

Updated under an hour ago (Oct 27, 2026, 1:40 AM ET)

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It affects Mozilla Firefox and 1 other product. Add what you run to find out whether that includes you.

EPSS puts the chance of exploitation in the next 30 days at 0.31%, higher than 24% of scored CVEs.

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Exploited in the last 30 days

Sandbox escape, site isolation issue due to incorrect boundary conditions, use-after-free in the Networking component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.

CVSS: 9.6 CRITICAL (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Weakness (CWE): CWE-416
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): 0.31% (percentile 24)
Assigned by: mozilla
NVD analysis: Deferred
Record last updated: Oct 13, 2026
First seen by InfoSec Signals: Oct 13, 2026

Affected products

Affected products

Mozilla Firefox mozilla:firefox (from the name)	153.5 builds before 153.* not affected; from 158 not affected	CNA record
Mozilla Thunderbird mozilla:thunderbird (from the name)	153.5 builds before 153.* not affected; from 158 not affected	CNA record

References

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2040905
https://www.mozilla.org/security/advisories/mfsa2026-106/
https://www.mozilla.org/security/advisories/mfsa2026-108/
https://www.mozilla.org/security/advisories/mfsa2026-109/
https://www.mozilla.org/security/advisories/mfsa2026-110/

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.