Acknowledgement: elixire vulnerability reported by Violet M. on 2020-05-03

Violet M. discovered a vulnerability on 2020-05-03 with our reverse proxy handling code and informed us through the mail address we specified on our security.txt.

We were using the X-Forwarded-For header for IP ratelimiting without realizing that IPs passed onto this aren't overridden by Cloudflare, but are appended. Relevant document can be found here.

This could potentially allow an attacker to bypass IP ratelimiting. We've deployed a fix shortly after she reported the issue to us:

We also deployed a workaround for our non-CF domains, which we will improve on v3. We did this by overriding the CF-Connecting-IP header with user's IP on nginx running on the routing server. We had been overriding X-Forwarded-For before this, so non-CF domains have been safe from this vulnerability the whole time.

Violet also found a potential vulnerability that an attacker with our IP addresses could abuse which was dependent on how our setup was configured behind the scenes, however this wasn't an issue that affected our specific setup as we have IP whitelists in place, and don't have as the default route on the routing server. Specifically, we limit to CF IPs on our routing server, and to routing server on the server that runs our elixire instance.

While the main instance at is safe from all these security issues now, we recommend anyone running elixire on their own server to upgrade to the latest master, and to deploy IP whitelists if they don't already have them in place (here's Cloudflare's IP list), and don't put elixire as your default route (as an attacker may put your IP to their Cloudflare account to bypass the whitelists). If you have a short list of domains, consider enabling Authenticated Origin Pulls.

We'd like to publicly thank Violet for helping us make elixire safer.

You may find/contact Violet at: