CVE-2026-103500 Heap buffer overflow opening large email
An attacker can trigger a heap buffer overflow by sending a large email, potentially leading to code execution or crashes in Thunderbird.
- 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-2026-103500?
CVE-2026-103500 is a medium-severity memory corruption vulnerability in Mozilla Thunderbird, published on 30 Sep 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
An attacker could cause a heap buffer overflow by getting a user to open an email that is greater than or equal to 2GB in size. This vulnerability was fixed in Thunderbird 157, Thunderbird 140.17, and Thunderbird 153.4.
Which versions are affected by CVE-2026-103500?
It affects 1 product.
Products include Mozilla Thunderbird.
How do I fix CVE-2026-103500?
Upgrade to a fixed version.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-103500 being exploited?
There is no known exploitation of CVE-2026-103500 in the wild and no public exploit code.
Other vulnerabilities in Mozilla Thunderbird
Sources
Also known as DEBIAN-CVE-2026-103500, GHSA-vjxp-5j85-5rqg, OESA-2026-4457, OESA-2026-4458, UBUNTU-CVE-2026-103500.