We recently received a detailed report from the Applied Cryptography Research Group at ETH Zurich describing several ways the CipherMail Gateway could be made to leak information about, or misrepresent the trust status of, the encrypted email it processes.
The vulnerabilities are related to S/MIME and PGP decryption.
For more information, see Five vulnerabilities in CipherMail Gateway: EFAIL revisited, a bounce oracle, and trust-tag spoofing - CipherMail Email Encryption
Users of the Enterprise/Pro edition can update directly (with dnf update from the command line).
Users of the Community edition can download the update from the Gitlab community page Releases · CipherMail B.V. / ciphermail-community-gateway · GitLab