## About Fancy Product Designer for WooCommerce
Fancy Product Designer for WooCommerce is a WordPress plugin which allows users
to design custom products in a vendor's WooCommerce store. It is sold through
the third-party marketplace "Envato Market" and boasts over 15,000 sales.
## Unrestricted File Upload
Fancy Product Designer for WooCommerce before and including version 4.5.1
contains an Unrestricted File Upload vulnerability.
An unauthenticated attacker is able to upload any type of file to an affected
WooCommerce store by exploiting a Time of Check, Time of Use (TOCTOU) weakness
in custom-image-handler.php's `url` parameter. However, the file will be saved
with one of the following extensions on the server: jpeg, png, or svg.
Fancy Product Designer for WooCommerce provides an option to require users to
log in before uploading images. However, an attacker is able to access the
custom-image-handler.php file directly and upload arbitrary files without
authentication.
### Details
The custom-image-handler.php file provides an interface where unauthenticated
users can provide the URL of an image and have that image saved on the server.
Before saving the file, custom-image-handler.php first checks the MIME type of
the file and confirms that it is one of the following: jpeg, png, or svg. Once
the file's MIME type has been verified, custom-image-handler.php downloads the
file a second time and saves the most recent copy to the filesystem with an
extension corresponding to the MIME type of the originally verified file.
This vulnerability can be exploited by sending a POST request to the following
URL of an affected WooCommerce site:
/wp-content/plugins/fancy-product-designer/inc/custom-image-handler.php
With this request, the following POST parameters should be sent as form data:
- saveOnServer: 1
- uploadsDirURL: https://[affected
site]/wp-content/uploads/fancy_products_uploads/
- uploadsDir: [full path to where the file should be saved on the server]
- url: [attacker-controlled URL]
The attacker-controlled URL should initially point to a valid file of type:
jpeg, png, or svg. Once a request has been made for the file, the attacker can
replace the file at the attacker-controlled URL with a malicious file, and the
malicious file will be saved on the server. The URL of the uploaded file will
then be returned to the attacker in response to the POST request.
Note: The default values for the `uploadsDirURL` and `uploadsDir` parameters
can be found by searching for the same strings in the source of any page using
an affected version of Fancy Product Designer for WooCommerce. Attackers are
also able to provide local file paths, which will cause FPD to copy the
specified file into the uploads directory if the file is one of the expected
types and the server is running with sufficient permissions to read the file.
### Impact
The fact that the uploaded file will have one of the previously mentioned
extensions greatly mitigates the impact of this vulnerability, as none of the
allowed extensions will be executed by the server. The following scenarios are
plausible by abusing this vulnerability:
- Stored XSS by uploading an SVG containing a malicious JavaScript payload
- Malware distribution by uploading malicious binaries and other payloads
### Proof of Concept
- Exploit code:
[poc.php](https://github.com/jdgregson/Disclosures/blob/master/fancy-product-designer/unrestricted-file-upload/poc.php)
- Demo video:
[unrestricted-file-upload.mp4](https://raw.githubusercontent.com/jdgregson/Disclosures/master/fancy-product-designer/unrestricted-file-upload/unrestricted-file-upload.mp4)
### Disclosure Timeline
- 10/11/2020: issue reported via ticket on developer's support forum
- 10/11/2020: ticket closed by developer with no response
- 10/20/2020: developer released an update which did not address the issue
- 10/26/2020: developer released an update which did not address the issue
- 11/14/2020: full disclosure
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