CVE-2026-100819 Sandbox escape due to incorrect boundary conditions in the XPCOM component
Attackers can escape the browser sandbox via incorrect boundary conditions in XPCOM, enabling code execution and privilege escalation.
- 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-2026-100819?
CVE-2026-100819 is a critical memory corruption vulnerability in Mozilla Firefox, published on 29 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
Sandbox escape due to incorrect boundary conditions in the XPCOM component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
Weakness: CWE-119
Which versions are affected by CVE-2026-100819?
It affects 2 products.
Products include Mozilla Firefox, Mozilla Thunderbird.
How do I fix CVE-2026-100819?
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-2026-100819 being exploited?
There is no known exploitation of CVE-2026-100819 in the wild and no public exploit code.
Other vulnerabilities in Mozilla Firefox
Sources
Also known as DEBIAN-CVE-2026-100819, GHSA-2x4q-w8v4-vwxh, UBUNTU-CVE-2026-100819.