Facing an issue with CMC that when someone tried to signup for newsletter on the site, it keeps waiting for response.

Did check the network tab and it makes an ajax call to :
/component/cmc/?format=raw&task=subscription.exist

and that throws error:
The most recent request was denied because it had an invalid security token. Please refresh the page and try again.

Narrowed it down to :
public_html/components/com_cmc/controllers/subscription.raw.php
and if i comment the session check on exist() & save() functions, the newsletter subscribe works perfectly.
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public function exist()
{
//JSession::checkToken() or jexit(JText::_('JINVALID_TOKEN'));

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Is there a way to fix the issue without modifying the core component.