CVE-2026-40203

Fixed in a distro release EPSS <1%CVSS 3.7

When IMAP compression is enabled, the same compression state is reused across responses in a session, so response sizes depend on both attacker-supplied mail and other mail in the same mailbox. An attacker that can send mail to a user and can also observe the sizes of that user's IMAP traffic can confirm whether the body of a small message matches a guessed text. Recovery of arbitrary unknown content was not demonstrated, but the attack can disclose whether a secret-like message body matches a candidate. Disable IMAP compression. Update to non-vulnerable version. No publicly available exploits are known.

Published 2026-08-28 · CVE record · OSV

Products: Open-Xchange GmbH OX Dovecot Pro, Open-Xchange GmbH OX Dovecot CE

Distro releases