Is CVE-2026-113866 being exploited?

No public exploit is currently tracked.

How severe is CVE-2026-113866?

CVE-2026-113866 has a CVSS v3 severity of MEDIUM (5.9).

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CVE-2026-113866

Description

When setting up an account, Thunderbird's Exchange AutoDiscover lookup also queried the domain's AutoDiscover service over plain HTTP. Due to a bug, that unencrypted request included the credentials the user had entered, allowing a network attacker to obtain the user's password. This vulnerability was fixed in Thunderbird 158.0.1 and Thunderbird 153.5.1.