CVE-2026-84142 Internally found bugs fixed in Thunderbird 155
Memory corruption and information disclosure flaws in Thunderbird allow attackers to potentially execute code or leak data, requiring an upgrade to version 155.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-84142?
CVE-2026-84142 is a critical memory corruption vulnerability in Mozilla Firefox, published on 1 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Internally found bugs present in Thunderbird 154. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155 and Thunderbird 155.
Which versions are affected by CVE-2026-84142?
It affects 2 products.
Products include Mozilla Firefox, Mozilla Thunderbird.
How do I fix CVE-2026-84142?
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-2026-84142 being exploited?
There is no known exploitation of CVE-2026-84142 in the wild and no public exploit code.
Other vulnerabilities in Mozilla Firefox
Sources
Also known as GHSA-jc69-hhhc-c4h9, UBUNTU-CVE-2026-84142.