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Bookwyrm Server Side Request Forgery

While reading the code of bookwyrm, i encounter this endpoint

This endpoint calls the function views.upload_cover.

You can see that it accepts a post request from the decorator above, and it requires authentication, which is not a problem since bookwyrm allow self registration. In the function, you can see that it takes a post parameter cover-url, and pass it through the function set_cover_from_url, then save the the cover of the book based on the returned value of set_cover_from_url.

In set_cover_from_url, it pass the url argument to the function get_image. Then, it generates a random image_name and return the image name and the content from the get_image function.

In theget_image function, it pass our url argument to requests.get and return the response. Making it vulnerable to ssrf.

So to test it out, i hosted my own bookworm instance and tested out the bug.

I put http://172.18.0.1/ in the cover-url which is the internal ip of my vps since my bookwyrm instance is hosted with docker. As you see, it responded with a redirect, just like what we expected

Now when we visit the cover of book 2, we will see this.

I host a wordpress instace on my vps and the response show a wordpress instance so this verifies that our ssrf works.

I tried achieving lfi with it, unfortunately, by default, requests.get of python doesnt accept the file:// scheme.

This is the end of the writeup, thanks for reading. Thank you to the maintainer of bookwyrm for being cooperative and responsive.

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This post is licensed under CC BY 4.0 by the author.