CVE-2026-4726 Denial-of-service in the XML component
An attacker can cause a denial of service in the XML component of Firefox and Thunderbird, requiring users to upgrade to version 149.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-4726?
CVE-2026-4726 is a high-severity denial of service vulnerability in Mozilla Firefox, published on 24 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Denial-of-service in the XML component. This vulnerability was fixed in Firefox 149 and Thunderbird 149.
Weakness: CWE-400
Which versions are affected by CVE-2026-4726?
It affects 2 products.
Products include Mozilla Firefox, Mozilla Thunderbird.
How do I fix CVE-2026-4726?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-4726 being exploited?
There is no known exploitation of CVE-2026-4726 in the wild and no public exploit code.
Other vulnerabilities in Mozilla Firefox
Sources
Also known as GHSA-2r77-x4qh-mhc3, UBUNTU-CVE-2026-4726.