CVE-2026-92240 Out-of-bounds read in IMAP response parser
A malicious IMAP server can crash Thunderbird via an out-of-bounds read in the response parser before authentication.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-92240?
CVE-2026-92240 is a critical memory corruption vulnerability in Mozilla Thunderbird, published on 15 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A malicious or compromised IMAP server can trigger an out-of-bounds read in the IMAP response parser by sending an untagged '* ID' response, crashing Thunderbird. The affected parsing path is reachable before authentication. This vulnerability was fixed in Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3.
Weakness: CWE-125
Which versions are affected by CVE-2026-92240?
It affects 1 product.
Products include Mozilla Thunderbird.
How do I fix CVE-2026-92240?
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-2026-92240 being exploited?
There is no known exploitation of CVE-2026-92240 in the wild and no public exploit code.
Other vulnerabilities in Mozilla Thunderbird
Sources
Also known as DEBIAN-CVE-2026-92240, GHSA-wq87-gp3m-ww5v, UBUNTU-CVE-2026-92240.