---
id: CVE-2026-100816
title: 'Site isolation issue in the DOM: Networking component'
summary: >-
  Site isolation issue in the DOM: Networking component. This vulnerability was
  fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 153.4, and Firefox
  157.
severity: high
cvss: 8.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N'
cwe:
  - CWE-346
vendor: mozilla
product: firefox
affected:
  - firefox < 153.4.0
  - 'firefox >= 154.0.0, < 157.0.0'
  - thunderbird < 153.4.0
  - 'thunderbird >= 154.0, < 157.0'
patched:
  - firefox 157.0.0
  - thunderbird 157.0
published: '2026-09-29'
updated: '2026-10-05'
sourceUpdated: '2026-10-05T16:59:58.540'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-100816'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=2068648'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-100/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-101/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-103/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-97/'
    label: security@mozilla.org
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-100816.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-100816'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2543147'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-100816'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-100816'
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-97/#CVE-2026-100816'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
  - score-dispute
epss: 0.00153
epssPercentile: 0.04383
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-01T15:38:39.482643Z'
ingestedAt: '2026-09-29T13:34:31.675Z'
scores:
  nvd: 8.1
  vendor: 6.1
---

## Overview

Site isolation issue in the DOM: Networking component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 153.4, and Firefox 157.

## Affected

- `firefox < 153.4.0`
- `firefox >= 154.0.0, < 157.0.0`
- `thunderbird < 153.4.0`
- `thunderbird >= 154.0, < 157.0`

## Remediation

Upgrade past the affected range:

- `firefox 157.0.0`
- `thunderbird 157.0`

## Vendor advisories

- **Red Hat VEX** · Moderate · updated 2026-10-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-100816.json)