Secuno
ENNL
Book demo

CVE-2026-8959

Mozilla Firefox buffer overflow

9.6 CRITICALEPSS 0.45%
  1. Published19 May 2026

Description

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionRequired
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Affected products

Mozilla Firefox< 151.0.0 · < 140.11.0
Mozilla Thunderbird< 151.0.0 · < 140.11

Remediation

Fixed in
Mozilla Firefox≥ 151.0.0
Mozilla Thunderbird≥ 151.0.0

References

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

CVE-2026-10910910.0
A vulnerability was detected in Wavlink WL-WN530BE1-A 251117. This vulnerability…
CVE-2026-962658.2
IBM Power Systems Firmware FW1060.00 through FW1060.81 is affected by a vulnerability…
CVE-2026-843198.3
Nginx UI is a web user interface for the Nginx web server. Prior to 2.4.1, the regular…
CVE-2026-843188.8
Nginx UI is a web user interface for the Nginx web server. From 2.0.0-rc.6 until 2.4.1,…
CVE-2026-843178.8
Nginx UI is a web user interface for the Nginx web server. Prior to 2.4.1,…
CVE-2026-843168.8
Nginx UI is a web user interface for the Nginx web server. Prior to 2.4.1,…

Frequently asked

Is CVE-2026-8959 being actively exploited?

CVE-2026-8959 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.45%.

How severe is CVE-2026-8959?

CVE-2026-8959 has a CVSS 3.1 base score of 9.6, rated critical. EPSS estimates a 0.45% probability of exploitation.

Which products are affected by CVE-2026-8959?

Affected products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-8959?

Upgrade affected software to a fixed version, for example Mozilla Firefox 151.0.0, Mozilla Thunderbird 151.0.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-8959 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation worksBook a demo

Get Patch this first every Monday

Five vulnerabilities that matter this week, ranked on real exploitation. Plain language, one email, no spam.

You can unsubscribe with one click from every issue. We handle your details as described in our privacy policy.

Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.