This script is possibly vulnerable to LDAP Injection attacks.
Lightweight Directory Access Protocol (LDAP) is an open-standard protocol for both querying and manipulating X.500 directory services. When a web application fails to properly sanitize user-supplied input, it is possible for an attacker to alter the construction of an LDAP statement.
When an attacker is able to modify an LDAP statement, the process will run with the same permissions as the component that executed the command. (e.g. Database server, Web application server, Web server, etc.). This can cause serious security problems where the permissions grant the rights to query, modify or remove anything inside the LDAP tree.
Your script should filter metacharacters from user input.