maddy is a composable, all-in-one mail server. Starting with version 0.2.0 and prior to version 0.6.3, maddy allows a full authentication bypass if SASL authorization username is specified when using the PLAIN authentication mechanisms. Instead of validating the specified username, it is accepted as is after checking the credentials for the authentication username. maddy 0.6.3 includes the fix for the bug. There are no known workarounds.
https://github.com/foxcpp/maddy/security/advisories/GHSA-4g76-w3xw-2x6w
https://github.com/foxcpp/maddy/releases/tag/v0.6.3
https://github.com/foxcpp/maddy/commit/9f58cb64b39cdc01928ec463bdb198c4c2313a9c
https://github.com/foxcpp/maddy/commit/55a91a37b71210f34f98f4d327c30308fe24399a