Security Puzzle (Log4J Edition)

private final DirContext context; //javax.naming.directory.DirContext

[...]

@SuppressWarnings("unchecked")
public <T> T lookup(final String name) throws NamingException {
public synchronized <T> T lookup(final String name) throws NamingException {

try {
    URI uri = new URI(name);
    if (uri.getScheme() != null) {
        if (!allowedProtocols.contains(uri.getScheme().toLowerCase(Locale.ROOT))) {
            LOGGER.warn("Log4j JNDI does not allow protocol {}", uri.getScheme());
            return null;
        }
        if (LDAP.equalsIgnoreCase(uri.getScheme()) || LDAPS.equalsIgnoreCase(uri.getScheme())) {
            if (!allowedHosts.contains(uri.getHost())) {
                LOGGER.warn("Attempt to access ldap server not in allowed list");
                return null;
            }
            Attributes attributes = this.context.getAttributes(name);
            if (attributes != null) {
                // In testing the "key" for attributes seems to be lowercase while the attribute id is
                // camelcase, but that may just be true for the test LDAP used here. This copies the Attributes
                // to a Map ignoring the "key" and using the Attribute's id as the key in the Map so it matches
                // the Java schema.
                Map<String, Attribute> attributeMap = new HashMap<>();
                NamingEnumeration<? extends Attribute> enumeration = attributes.getAll();
                while (enumeration.hasMore()) {
                    Attribute attribute = enumeration.next();
                    attributeMap.put(attribute.getID(), attribute);
                }
                Attribute classNameAttr = attributeMap.get(CLASS_NAME);
                if (attributeMap.get(SERIALIZED_DATA) != null) {
                    if (classNameAttr != null) {
                        String className = classNameAttr.get().toString();
                        if (!allowedClasses.contains(className)) {
                            LOGGER.warn("Deserialization of {} is not allowed", className);
                            return null;
                        }
                    } else {
                        LOGGER.warn("No class name provided for {}", name);
                        return null;
                    }
                } else if (attributeMap.get(REFERENCE_ADDRESS) != null
                        || attributeMap.get(OBJECT_FACTORY) != null) {
                    LOGGER.warn("Referenceable class is not allowed for {}", name);
                    return null;
                }
            }
        }
    }
} catch (URISyntaxException ex) {
    // This is OK.
}
return (T) this.context.lookup(name);

}