CodeIgniter4 has a validation bypass when uploading file extensions via ext_in rule
Impact
Theext_in upload validation rule checked the MIME-derived guessed extension instead of the client-provided filename extension. As a result, an uploaded file named shell.php containing GIF-like content could pass validation such as:
uploaded[avatar]|is_image[avatar]|mime_in[avatar,image/gif]|ext_in[avatar,gif]gif, even though the uploaded filename extension is php.Applications are impacted if they:
- accept user-controlled uploads,
- rely on
ext_into validate the uploaded filename extension, - save uploaded files using the original client filename:
$file->move($path), - store uploads in a web-accessible directory,
- and allow PHP or other executable files to run from that directory.
In those conditions, this may lead to arbitrary code execution. The default application does not expose such an upload endpoint.
Patches
Upgrade to v4.7.3 or later.Workarounds
- Save uploads outside the public web root, preferably under
writable/uploads - Use
$file->store()or$file->move($path, $file->getRandomName())instead of preserving the original filename - Disable script execution in any public upload directory
- Manually verify the client filename extension before moving the file
- Reject files when
$file->getClientExtension()is not in the allowed list or does not match$file->guessExtension()