CVE-2026-12315 Mitigation bypass in the DOM: Security component

Critical 9.1 Published 16 Jun 2026 Updated 16 Jun 2026

An attacker can bypass DOM security mitigations in Firefox and Thunderbird, potentially enabling further exploitation of the browser environment.

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

What is CVE-2026-12315?

CVE-2026-12315 is a critical vulnerability in Mozilla Firefox, published on 16 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12.

Weakness: CWE-693

Which versions are affected by CVE-2026-12315?

It affects 2 products.

Products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-12315?

Upgrade to a fixed version.

Is CVE-2026-12315 being exploited?

There is no known exploitation of CVE-2026-12315 in the wild and no public exploit code.

All Mozilla Firefox vulnerabilities

Sources

Also known as DEBIAN-CVE-2026-12315, GHSA-9j9w-q224-vc26, UBUNTU-CVE-2026-12315.