Magento had not correctly set concurrent sessions to expire. A customer could log out under the mistaken assumption that their sessions had expired, but later, an attacker could access the account through one of the unexpired sessions.
Part of patch: MAGENTO 2.0.16 AND 2.1.9 SECURITY UPDATE
This vulnerability affects the following application versions:
- Magento 2.1.5
- Magento 2.1.6
- Magento 2.1.7
- Magento 2.1.8