CVE-2026-110249 Denial-of-service in the Exchange email component
A malicious Exchange server can cause Thunderbird to hang for extended periods by sending a crafted SOAP response, requiring an upgrade to fix.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-110249?
CVE-2026-110249 is a high-severity denial of service vulnerability in Mozilla Thunderbird, published on 13 Oct 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
A malicious, compromised, or MITM-controlled Exchange server can return a single well-formed SOAP response containing an element with enough attributes to keep Thunderbird's main thread CPU-bound for seconds to hours. This vulnerability was fixed in Thunderbird 158 and Thunderbird 153.5.
Weakness: CWE-400
Which versions are affected by CVE-2026-110249?
How do I fix CVE-2026-110249?
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-2026-110249 being exploited?
There is no known exploitation of CVE-2026-110249 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-110249, GHSA-3vgg-r2jh-qqpj, UBUNTU-CVE-2026-110249.