CVE-2026-33603

A flaw was found in Dovecot. An attacker, positioned as a Man-in-the-Middle (MITM) between Dovecot and a client, can exploit a specially crafted base64 exchange to fake SCRAM TLS channel binding. This allows the attacker to eavesdrop on communications between Dovecot and the client, leading to information disclosure.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To reduce the risk of a Man-in-the-Middle attack, restrict network access to the Dovecot server. Configure firewalls to permit connections only from trusted networks and necessary client IP ranges. This limits an attacker's ability to intercept traffic. If firewall rules are modified, a service reload or restart may be required, which could temporarily disrupt active user sessions.