CVE-2026-0877 Mitigation bypass in the DOM: Security component

What is CVE-2026-0877?

CVE-2026-0877 is a high-severity vulnerability in Mozilla Firefox, published on 13 Jan 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

Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 147, Firefox ESR 115.32, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

Weakness: CWE-693

Which versions are affected by CVE-2026-0877?

It affects 2 products.

Products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-0877?

Upgrade to a fixed version.

Is CVE-2026-0877 being exploited?

There is no known exploitation of CVE-2026-0877 in the wild and no public exploit code.

Other vulnerabilities in Mozilla Firefox

• CVE-2019-11708 Mozilla Firefox and Thunderbird Sandbox Escape Exploited Critical 10.0
• CVE-2010-3765 Mozilla Multiple Products Remote Code Execution Exploited Critical 9.8
• CVE-2022-26486 Mozilla Firefox Use-After-Free Exploited Critical 9.6
• CVE-2022-26485 Mozilla Firefox Use-After-Free Exploited High 8.8
• CVE-2019-11707 Mozilla Firefox and Thunderbird Type Confusion Exploited High 8.8

All Mozilla Firefox vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2026-0877, GHSA-rfgw-g9g4-685p, UBUNTU-CVE-2026-0877.