Quoting upstream PostgreSQL security page: http://www.postgresql.org/support/security.html
If PostgreSQL is configured with LDAP authentication, and your LDAP configuration allows anonymous binds, it is possible for a user to authenticate themselves with an empty password.
Affected versions: 8.3, 8.2
Fixed in versions: 8.3.8, 8.2.14
Severity: A - A vulnerability that is exploitable for privilege escalation without requiring a prior login.