CVE-2026-84640

A vulnerability exists in certain versions of Thunderbird where a specially crafted mail header can cause a one-byte read past the end of a buffer, potentially leading to information disclosure or application instability. Users of affected Thunderbird versions should prioritize updating to Thunderbird 155, 140.15, or 153.2 to mitigate this risk. Organizations relying on Thunderbird for email communication should assess their deployments and ensure they are running the patched versions.