---
id: CVE-2026-0877
title: 'Mitigation bypass in the DOM: Security component'
summary: >-
  Mitigation bypass in the DOM: Security component. This vulnerability was fixed
  in Firefox 147, Firefox ESR 115.32, Firefox ESR 140.7, Thunderbird 147, and
  Thunderbird 140.7.
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-693
vendor: mozilla
product: firefox
affected:
  - firefox < 115.32.0
  - firefox < 147.0
  - 'firefox >= 128.0, < 140.7.0'
  - thunderbird < 140.7.0
  - thunderbird < 147.0
patched:
  - firefox 140.7.0
  - thunderbird 147.0
published: '2026-01-13'
updated: '2026-06-30'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-0877'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1999257'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-01/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-02/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-03/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-04/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-05/'
    label: security@mozilla.org
  - url: 'https://access.redhat.com/errata/RHSA-2026:0667'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:0694'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:0924'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:1320'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:1413'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:1414'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:1415'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:1461'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:1462'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:1471'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:1487'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2041'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2043'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2044'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2047'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2069'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2070'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2073'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2074'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2220'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2231'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2271'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:2286'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/security/cve/CVE-2026-0877'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2428969'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-0877.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-0877'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-0877'
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-03/#CVE-2026-0877'
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-05/#CVE-2026-0877'
tags:
  - nvd
  - csaf
  - vex
  - red-hat
epss: 0.00473
epssPercentile: 0.40709
ingestedAt: '2026-06-30T13:26:50.454Z'
scores:
  nvd: 8.1
  vendor: 7.5
---

## Overview

Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 147, Firefox ESR 115.32, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

## Affected

- `firefox < 115.32.0`
- `firefox < 147.0`
- `firefox >= 128.0, < 140.7.0`
- `thunderbird < 140.7.0`
- `thunderbird < 147.0`

## Remediation

Upgrade past the affected range:

- `firefox 140.7.0`
- `thunderbird 147.0`

## Vendor advisories

- **RHSA-2026:2231** · Red Hat · fixed in: Red Hat Enterprise Linux Server (v. 7 ELS) · released 2026-02-09 · [advisory](https://access.redhat.com/errata/RHSA-2026:2231)
- **RHSA-2026:2271** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream EUS (v. 10.0), Red Hat Enterprise Linux AppStream (v. 10) · released 2026-02-09 · [advisory](https://access.redhat.com/errata/RHSA-2026:2271)
- **RHSA-2026:2286** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream EUS (v. 10.0), Red Hat Enterprise Linux AppStream (v. 10) · released 2026-02-09 · [advisory](https://access.redhat.com/errata/RHSA-2026:2286)
- **RHSA-2026:0667** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 8) · released 2026-01-15 · [advisory](https://access.redhat.com/errata/RHSA-2026:0667)
- **RHSA-2026:2220** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 8) · released 2026-02-09 · [advisory](https://access.redhat.com/errata/RHSA-2026:2220)
- **RHSA-2026:2074** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream AUS (v. 8.2) · released 2026-02-05 · [advisory](https://access.redhat.com/errata/RHSA-2026:2074)
- **RHSA-2026:1471** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream AUS (v. 8.2) · released 2026-01-28 · [advisory](https://access.redhat.com/errata/RHSA-2026:1471)
- **RHSA-2026:2073** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream AUS (v.8.4), Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) · released 2026-02-05 · [advisory](https://access.redhat.com/errata/RHSA-2026:2073)
- **RHSA-2026:1461** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream AUS (v.8.4), Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) · released 2026-01-28 · [advisory](https://access.redhat.com/errata/RHSA-2026:1461)
- **RHSA-2026:2070** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream AUS (v.8.6), Red Hat Enterprise Linux AppStream E4S (v.8.6), Red Hat Enterprise Linux AppStream TUS (v.8.6) · released 2026-02-05 · [advisory](https://access.redhat.com/errata/RHSA-2026:2070)
- **RHSA-2026:1487** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream AUS (v.8.6), Red Hat Enterprise Linux AppStream E4S (v.8.6), Red Hat Enterprise Linux AppStream TUS (v.8.6) · released 2026-01-28 · [advisory](https://access.redhat.com/errata/RHSA-2026:1487)
- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 10 · updated 2026-10-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-0877.json)