Description
Impact
The ext_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]
because the detected MIME type maps to gif, even though the uploaded filename extension is php.
Applications are impacted if they:
- accept user-controlled uploads,
- rely on
ext_in to 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()
Resources
NVD description
CodeIgniter is a PHP full-stack web framework. Prior to 4.7.3, the ext_in upload validation rule in system/Validation/StrictRules/FileRules.php 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] because the detected MIME type maps to gif, even though the uploaded filename extension is php. Applications are impacted if they accept user-controlled uploads, rely on ext_in to validate the uploaded filename extension, save uploaded files using the original client filename with $file->move($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. This issue is fixed in version 4.7.3.
Running one of these products? Scan your site to see whether it exposes a vulnerable version.
Scan my site free