CVE-2026-8949 Integer overflow in the Widget: Win32 component

High 7.5 Published 19 May 2026 Updated 19 May 2026

An integer overflow in the Win32 widget component allows attackers to potentially execute arbitrary code, requiring users to upgrade their browsers.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-8949?

CVE-2026-8949 is a high-severity vulnerability in Mozilla Firefox, published on 19 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Integer overflow in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

Weakness: CWE-190

Which versions are affected by CVE-2026-8949?

It affects 2 products.

Products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-8949?

Upgrade to a fixed version.

Is CVE-2026-8949 being exploited?

There is no known exploitation of CVE-2026-8949 in the wild and no public exploit code.

All Mozilla Firefox vulnerabilities

Sources

Also known as GHSA-wpxg-v53p-m79m, UBUNTU-CVE-2026-8949.