The bind operation of LDAP, as described in RFC 4513, provides a method
which allows for authentication of users. For the Simple Authentication
Method a user may use the anonymous authentication mechanism, the
unauthenticated authentication mechanism, or the name/password
authentication mechanism. The unauthenticated authentication mechanism
is used when a client who desires to establish an anonymous
authorization state passes a non-zero length distinguished name and a
zero length password. Most LDAP servers either can be configured to
allow this mechanism or allow it by default.

_Web-based applications which perform the simple bind operation with the
client's credentials are at risk when an anonymous authorization state is
established. This can occur when the web-based application passes a
distinguished name and a zero length password to the LDAP server._

Thus, misconfiguring a server with simple bind can trick Symfony into
thinking the username/password tuple as valid, potentially leading to
unauthorized access.