CVE-2026-12296 Sandbox escape in the Security: Process Sandboxing component

Critical 9.6 Published 16 Jun 2026 Updated 15 Jul 2026

Attackers can escape the process sandbox to execute arbitrary code or escalate privileges, affecting Firefox and Thunderbird users.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: Available

What is CVE-2026-12296?

CVE-2026-12296 is a critical vulnerability in Mozilla Firefox, published on 16 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

Sandbox escape in the Security: Process Sandboxing component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12.

Weakness: CWE-403, CWE-693

Which versions are affected by CVE-2026-12296?

It affects 2 products.

Products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-12296?

Upgrade to a fixed version.

Is CVE-2026-12296 being exploited?

There is no known exploitation of CVE-2026-12296 in the wild and no public exploit code.

All Mozilla Firefox vulnerabilities

Sources

Also known as DEBIAN-CVE-2026-12296, GHSA-2xx6-2jh9-8wmx, UBUNTU-CVE-2026-12296.