In the last few days two new releases of Mail-in-a-Box were posted correcting two moderate security issues, one since v0.18 and the other since v0.19.
The current release is v0.19b. Everyone should upgrade.
The change log showing the two fixes is at https://github.com/mail-in-a-box/mailinabox/blob/v0.19b/CHANGELOG.md.
Upgrade instructions: https://mailinabox.email/maintenance.html#upgrade