CVE-2026-40193: Maddy Mail Server has an LDAP Filter Injection via Unsanitized Username

The auth.ldap module constructs LDAP search filters and DN strings by directly interpolating user-supplied usernames via strings.ReplaceAll() without any LDAP filter escaping. An attacker who can reach the SMTP submission (AUTH PLAIN) or IMAP LOGIN interface can inject arbitrary LDAP filter expressions through the username field, enabling identity spoofing, LDAP directory enumeration, and attribute value extraction. The go-ldap/ldap/v3 library—already imported in the same file—provides ldap.EscapeFilter() specifically for this purpose, but it is never called.