We are seeing an old vulnerability on e107 being widely scanned and exploited. e107 is a free open source content management system (CMS).
More details on the vulnerability are available here:
It was discovered that access control to the [php] bbcode which allows executing PHP code is wrongly implemented in e107. This allows unauthenticated users to execute arbitrary PHP code easily.
Affected is e107 < = 0.7.20