Cache Deception Armor
Before learning about Cache Deception Armor, you should first understand how Web Cache Deception attacks work.
Web Cache Deception attacks
Web Cache Deceptions attacks occur when an attacker tricks a user into opening a link in the format of
http://www.example.com/newsfeed is the location of a dynamic script that returns different content for different users.
This scenario becomes problematic when your website is configured to be flexible about what kinds of paths it can handle. To be more specific, when requests to a path that do not exist, such as
/x/y/z are treated as equivalent to requests to a parent path that does exist
For example, an attacker could send a user a link to
http://www.example.com/newsfeed/foo.jpg so that the user could be taken to their newsfeed. When the request passes through Cloudflare, the request would be cached because the path ends in
.jpg. The attacker can then visit the same URL themselves, and their request will be served from Cloudflare’s cache, exposing your user’s sensitive content.
Cache Deception Armor protects against attacks
You can protect users from Web Cache Deception attacks by adding a Cache Deception Armor Page Rule. With this rule, you can continue to cache static assets, but the rule will verify a URL’s extension matches the returned
In the newsfeed example above, if
http://www.example.com/newsfeed is a script that outputs a web page, the
text/html. On the other hand,
http://www.example.com/newsfeed/foo.jpg is expected to have
Content-Type. When a mismatch that could result in a Web Cache Deception attack is found, Cloudflare does not cache the response.
- If the returned
application/octet-stream, the extension does not matter because that is typically a signal to instruct the browser to save the asset instead of to display it.
- Cloudflare allows
.jpgto be served as
video/webmand other cases that we think are unlikely to be attacks.
- Keep in mind that Cache Deception Armor depends upon Origin Cache Control. A
Cache-Controlheader from the origin, Edge Cache TTL Page Rule or Browser Cache TTL zone setting may override the protection.
Enable Cache Deception Armor
To enable Cache Deception Armor, you need to start by creating a Page Rule. Follow the steps bellow for guidance:
- Log in to your Cloudflare dashboard, and select your account and domain.
- Select Rules > Page Rules.
- Select Create Page Rule.
- Enter the URL information and choose Cache Deception Armor from the dropdown menu.
- Enable Cache Deception Armor .
- Select Save and Deploy when you are done.