CVE-2026-84121
published 2026-09-01CVE-2026-84121: Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15…
PriorityP349critical9.6CVSS 3.1
AVNACLPRNUIRSCCHIHAH
EPSS
0.32%
24.6th percentile
Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
Affected
18 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| mozilla | firefox | < Firefox 155 | Firefox 155 |
| mozilla | firefox | < 115.40.0 | 115.40.0 |
| mozilla | firefox | — | — |
| mozilla | firefox | >= 116.0 < 140.15.0 | 140.15.0 |
| mozilla | firefox | >= 141.0.0 < 153.2.0 | 153.2.0 |
| mozilla | firefox | >= 154.0.0 < 155.0.0 | 155.0.0 |
| mozilla | firefox_esr | < Firefox ESR 140.15 | Firefox ESR 140.15 |
| mozilla | firefox_esr | < Firefox ESR 115.40 | Firefox ESR 115.40 |
| mozilla | firefox_esr | < Firefox ESR 153.2 | Firefox ESR 153.2 |
| mozilla | thunderbird | < Thunderbird 155 | Thunderbird 155 |
| mozilla | thunderbird | < Thunderbird 140.15 | Thunderbird 140.15 |
| mozilla | thunderbird | < Thunderbird 153.2 | Thunderbird 153.2 |
| mozilla | thunderbird | < 140.15.0 | 140.15.0 |
| mozilla | thunderbird | — | — |
| mozilla | thunderbird | >= 141.0 < 153.2.0 | 153.2.0 |
| mozilla | thunderbird | >= 154.0 < 155.0 | 155.0 |
| rhel10 | firefox-flatpak | — | — |
| rhel10 | thunderbird-flatpak | — | — |
CVSS provenance
nvdv3.19.6CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
vendor_redhat9.6CRITICAL
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Red Hat
firefox: Sandbox escape due to use-after-free in the DOM: Security component
vendor_redhat·2026-09-01·CVSS 9.6
CVE-2026-84121 [CRITICAL] CWE-825 firefox: Sandbox escape due to use-after-free in the DOM: Security component
firefox: Sandbox escape due to use-after-free in the DOM: Security component
Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
A flaw was found in Firefox. The Mozilla Foundation's Security Advisory describes the following issue:
Sandbox escape due to use-after-free in the DOM: Security component
Statement: Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.
Package: firefox (Red Hat Enterprise Linux 10) - Affected
Package: rhel10/firefox-flatpak (Red Hat Enterprise Linux 10) - Affected
Package: rhel10/thunderbird-flatpak (Red Hat Enterprise
Mozilla
Mozilla Foundation Security Advisory 2026-86: CVE-2026-84121
vendor_mozilla·CVSS 9.6
CVE-2026-84121 [CRITICAL] Mozilla Foundation Security Advisory 2026-86: CVE-2026-84121
Mozilla Foundation Security Advisory 2026-86
CVE: CVE-2026-84121
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 155
Mozilla
Mozilla Foundation Security Advisory 2026-84: CVE-2026-84121
vendor_mozilla·CVSS 9.6
CVE-2026-84121 [CRITICAL] Mozilla Foundation Security Advisory 2026-84: CVE-2026-84121
Mozilla Foundation Security Advisory 2026-84
CVE: CVE-2026-84121
Product: Firefox ESR
Impact: high
Fixed in: Firefox ESR 140.15
Mozilla
Mozilla Foundation Security Advisory 2026-87: CVE-2026-84121
vendor_mozilla·CVSS 9.6
CVE-2026-84121 [CRITICAL] Mozilla Foundation Security Advisory 2026-87: CVE-2026-84121
Mozilla Foundation Security Advisory 2026-87
CVE: CVE-2026-84121
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 140.15
Mozilla
Mozilla Foundation Security Advisory 2026-83: CVE-2026-84121
vendor_mozilla·CVSS 9.6
CVE-2026-84121 [CRITICAL] Mozilla Foundation Security Advisory 2026-83: CVE-2026-84121
Mozilla Foundation Security Advisory 2026-83
CVE: CVE-2026-84121
Product: Firefox ESR
Impact: high
Fixed in: Firefox ESR 115.40
Mozilla
Mozilla Foundation Security Advisory 2026-85: CVE-2026-84121
vendor_mozilla·CVSS 9.6
CVE-2026-84121 [CRITICAL] Mozilla Foundation Security Advisory 2026-85: CVE-2026-84121
Mozilla Foundation Security Advisory 2026-85
CVE: CVE-2026-84121
Product: Firefox ESR
Impact: high
Fixed in: Firefox ESR 153.2
Mozilla
Mozilla Foundation Security Advisory 2026-82: CVE-2026-84121
vendor_mozilla·CVSS 9.6
CVE-2026-84121 [CRITICAL] Mozilla Foundation Security Advisory 2026-82: CVE-2026-84121
Mozilla Foundation Security Advisory 2026-82
CVE: CVE-2026-84121
Product: Firefox
Impact: high
Fixed in: Firefox 155
Mozilla
Mozilla Foundation Security Advisory 2026-88: CVE-2026-84121
vendor_mozilla·CVSS 9.6
CVE-2026-84121 [CRITICAL] Mozilla Foundation Security Advisory 2026-88: CVE-2026-84121
Mozilla Foundation Security Advisory 2026-88
CVE: CVE-2026-84121
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 153.2
GHSA
Sandbox escape due to use-after-free in the DOM: Security component.
ghsa_unreviewed·2026-09-01
CVE-2026-84121 [CRITICAL] CWE-416 Sandbox escape due to use-after-free in the DOM: Security component.
Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2.
No detection rules found.
No public exploits indexed.
Bugzilla
CVE-2026-84121 firefox: Sandbox escape due to use-after-free in the DOM: Security component
bugzilla·2026-09-01·CVSS 9.6
CVE-2026-84121 [CRITICAL] CVE-2026-84121 firefox: Sandbox escape due to use-after-free in the DOM: Security component
CVE-2026-84121 firefox: Sandbox escape due to use-after-free in the DOM: Security component
Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2.
Hackernews
⚡ Weekly Recap: Chrome 0-Day, Router Hijacks, Coder Supply Chain Attack and More
blogs_hackernews·2026-09-07·CVSS 6.9
CVE-2026-86206 [MEDIUM] ⚡ Weekly Recap: Chrome 0-Day, Router Hijacks, Coder Supply Chain Attack and More
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## ⚡ Weekly Recap: Chrome 0-Day, Router Hijacks, Coder Supply Chain Attack and More
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2026-09-01
Published