Potential access to sensitive URLs via CKAN extensions (SSRF)

Impact

There are a number of CKAN plugins, including XLoader, DataPusher, Resource proxy and ckanext-archiver, that work by downloading the contents of local or remote files in order to perform some actions with their contents (e.g. pushing to the DataStore, streaming contents or saving a local copy). All of them use the resource URL, and there are currently no checks to limit what URLs can be requested. This means that a malicious (or unaware) user can create a resource with a URL pointing to a place where they should not have access in order for one of the previous tools to retrieve it (known as a Server Side Request Forgery).

Patches and Workarounds

Users wanting to protect against these kinds of attacks can use one or a combination of the following approaches:

• Use a separate HTTP proxy like Squid that can be used to allow / disallow IPs, domains etc as needed, and make CKAN extensions aware of this setting via the ckan.download_proxy config option.
• Implement custom firewall rules to prevent access to restricted resources.
• Use custom validators on the resource url field to block/allow certain domains or IPs.

All latest versions of the plugins linked above support the ckan.download_proxy settings. Support for this setting in the Resource Proxy plugin was included in CKAN 2.10.5 and 2.11.0

References

• Blog post provides more details on how to configure a Squid proxy to prevent these issues