They immediately contacted Woo about the issue and Woo released a fix this morning with their release of WooCommerce version 2.3.6. We strongly recommend you immediately upgrade if you have not already.
The specific issue is an SQL injection vulnerability in the admin panel. Within the Tax Settings page of WooCommerce, the key of the ‘tax_rate_country’ POST parameter is passed unescaped into a SQL insert statement. For example, a payload of
tax_rate_country[(SELECT SLEEP(10))] would cause the MySQL server to sleep for 10 seconds.
Because this vulnerability requires either a Shop Manager or Admin user account, it would need to be combined with an XSS attack in order to be exploited.
What to do: Upgrade immediately to version 2.3.6 of WooCommerce which contains the fix.
Huge thanks to the WooThemes team for immediately addressing the issue and pushing the fix within a few HOURS of receiving the report.