---
title: "CVE-2026-109705: Mozilla Firefox - Use After Free"
description: "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."
url: https://panop.io/threat-heartbeat/CVE-2026-109705/
---

# 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 ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-109705)

## 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](https://cwe.mitre.org/data/definitions/416.html)

## 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

- [https://nvd.nist.gov/vuln/detail/CVE-2026-109705](https://nvd.nist.gov/vuln/detail/CVE-2026-109705)
- [https://bugzilla.mozilla.org/show\_bug.cgi?id=2040905](https://bugzilla.mozilla.org/show_bug.cgi?id=2040905)
- [https://www.mozilla.org/security/advisories/mfsa2026-106/](https://www.mozilla.org/security/advisories/mfsa2026-106/)
- [https://www.mozilla.org/security/advisories/mfsa2026-108/](https://www.mozilla.org/security/advisories/mfsa2026-108/)
- [https://www.mozilla.org/security/advisories/mfsa2026-109/](https://www.mozilla.org/security/advisories/mfsa2026-109/)
- [https://www.mozilla.org/security/advisories/mfsa2026-110/](https://www.mozilla.org/security/advisories/mfsa2026-110/)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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