CVE-2026-8959
published 2026-05-19CVE-2026-8959: Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11…
PriorityP346critical9.6CVSS 3.1
AVNACLPRNUIRSCCHIHAH
EPSS
0.42%
33.8th percentile
Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.
Affected
10 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| mozilla | firefox | < Firefox 151 | Firefox 151 |
| mozilla | firefox | < 140.11.0 | 140.11.0 |
| mozilla | firefox | < 151.0.0 | 151.0.0 |
| mozilla | firefox | — | — |
| mozilla | firefox_esr | < Firefox ESR 140.11 | Firefox ESR 140.11 |
| mozilla | thunderbird | < Thunderbird 140.11 | Thunderbird 140.11 |
| mozilla | thunderbird | < Thunderbird 151 | Thunderbird 151 |
| mozilla | thunderbird | < 140.11 | 140.11 |
| mozilla | thunderbird | < 151.0.0 | 151.0.0 |
| rhel10 | firefox-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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VulDB
Mozilla Firefox up to 140.10/150 Win32 sandbox
vuldb·2026-05-19·CVSS 9.6
CVE-2026-8959 [CRITICAL] Mozilla Firefox up to 140.10/150 Win32 sandbox
A vulnerability classified as critical has been found in Mozilla Firefox up to 140.10/150. Affected is an unknown function of the component Win32. Performing a manipulation results in sandbox issue.
This vulnerability is identified as CVE-2026-8959. The attack can be initiated remotely. There is not any exploit available.
It is recommended to upgrade the affected component.
GHSA
GHSA-3x92-cxc7-h2pw: Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component
ghsa_unreviewed·2026-05-19
CVE-2026-8959 [CRITICAL] CWE-20 GHSA-3x92-cxc7-h2pw: Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component
Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151 and Firefox ESR 140.11.
Red Hat
firefox: Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component
vendor_redhat·2026-05-19·CVSS 9.6
CVE-2026-8959 [CRITICAL] CWE-653 firefox: Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component
firefox: Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component
A flaw was found in Firefox. The Mozilla Foundation's Security Advisory describes the following issue:
Sandbox escape due to incorrect boundary conditions in the Widget: Win32 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: firefox (Red Hat Enterprise Linux 6) - Out of support scope
Package: firefox (Red Hat Enterprise Linux 7) - Affected
Package: firefox (Red Hat Enterprise Linux 8) - Affected
Package: firefox (Red Hat Enterprise Linux 9) - Affected
Mozilla
Mozilla Foundation Security Advisory 2026-48: CVE-2026-8959
vendor_mozilla·CVSS 9.6
CVE-2026-8959 [CRITICAL] Mozilla Foundation Security Advisory 2026-48: CVE-2026-8959
Mozilla Foundation Security Advisory 2026-48
CVE: CVE-2026-8959
Product: Firefox ESR
Impact: high
Fixed in: Firefox ESR 140.11
Mozilla
Mozilla Foundation Security Advisory 2026-51: CVE-2026-8959
vendor_mozilla·CVSS 9.6
CVE-2026-8959 [CRITICAL] Mozilla Foundation Security Advisory 2026-51: CVE-2026-8959
Mozilla Foundation Security Advisory 2026-51
CVE: CVE-2026-8959
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 140.11
Mozilla
Mozilla Foundation Security Advisory 2026-50: CVE-2026-8959
vendor_mozilla·CVSS 9.6
CVE-2026-8959 [CRITICAL] Mozilla Foundation Security Advisory 2026-50: CVE-2026-8959
Mozilla Foundation Security Advisory 2026-50
CVE: CVE-2026-8959
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 151
Mozilla
Mozilla Foundation Security Advisory 2026-46: CVE-2026-8959
vendor_mozilla·CVSS 9.6
CVE-2026-8959 [CRITICAL] Mozilla Foundation Security Advisory 2026-46: CVE-2026-8959
Mozilla Foundation Security Advisory 2026-46
CVE: CVE-2026-8959
Product: Firefox
Impact: high
Fixed in: Firefox 151
No detection rules found.
No public exploits indexed.
2026-05-19
Published