CVE-2026-109773 Denial-of-service in the Sync component
An attacker can cause a denial of service in the Sync component of Firefox and Thunderbird, requiring users to upgrade to version 158.
- 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-2026-109773?
CVE-2026-109773 is a medium-severity denial of service vulnerability in Mozilla Firefox, published on 13 Oct 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
Denial-of-service in the Sync component. This vulnerability was fixed in Firefox 158 and Thunderbird 158.
Weakness: CWE-400
Which versions are affected by CVE-2026-109773?
How do I fix CVE-2026-109773?
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-2026-109773 being exploited?
There is no known exploitation of CVE-2026-109773 in the wild and no public exploit code.
Sources
Also known as GHSA-79xh-524x-68c3, UBUNTU-CVE-2026-109773.