CVE-2026-74939 Privilege escalation in the DOM: Navigation component
Attackers can escalate privileges via the DOM Navigation component in Firefox and Thunderbird, requiring users to upgrade to patched versions.
- 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-2026-74939?
CVE-2026-74939 is a high-severity vulnerability in Mozilla Firefox, published on 18 Aug 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
Privilege escalation in the DOM: Navigation component. This vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.
Weakness: CWE-269
Which versions are affected by CVE-2026-74939?
It affects 2 products.
Products include Mozilla Firefox, Mozilla Thunderbird.
How do I fix CVE-2026-74939?
Upgrade to a fixed version.
Is CVE-2026-74939 being exploited?
There is no known exploitation of CVE-2026-74939 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in Mozilla Firefox
Sources
Also known as DEBIAN-CVE-2026-74939, GHSA-mcwh-jxcv-xq9h, UBUNTU-CVE-2026-74939.