Advance Guest Post <= 1.9 - Unauthenticated Arbitrary File Upload via gallery_action
The Advance Guest Post WordPress plugin through 1.9 does not properly validate uploaded files, relying on a case-sensitive and incomplete extension check that unauthenticated users can trivially bypass, allowing them to upload arbitrary files, including executable PHP variants, into a web-reachable directory, which can lead to remote code execution depending on the server configuration.