[jacobian]

Yup, that's basically it. It essentially makes phishing Django sites easier. The vulnerability could allow an attacker to send a legit email -- sent by the real site itself -- with a link that sends a user to a malicious site instead.

[So please upgrade!]

[gojomo]

The fix as described seems to just check the Host header for suspiciously-formatted information. Is that also enough to prevent other wrong (but well-formatted) Host values from being used?

It seems to me that the deeper risk is composing emails based on a passed Host value, rather than any sort of canonical name the site has for itself. Does the warning about avoiding domain-wildcard setups mean this is still a risk, even after the latest fix?

[jacobian]

> The fix as described seems to just check the Host header for suspiciously-formatted information. Is that also enough to prevent other wrong (but well-formatted) Host values from being used?

No, it's not. As the release notes say, "Some attacks against this are beyond Django's ability to control, and require the web server to be properly configured"; see https://docs.djangoproject.com/en/1.4/topics/security/#host-... for details.

[gojomo]

Thanks for the clarification.

The note about "beyond Django's ability to control" seems hand-wavey to me. Avoiding the use of the Host header to construct URLs -- not necessarily as a quick fix, but as a long-term better-practices goal -- would put safety against such attacks completely under Django's control, and provide a bit more defense-in-depth.

[eli]

But most sites need to work from at least two hostnames (dev and production). So would you need to set up a whitelist in advance?

[gojomo]

Not exactly, but sort of.

My estimation of what would be most safe/robust would be for a deployment to know its own canonical hostname/base-URL, and use that trusted value in construction of emailed URLs.

Perhaps this would be one of the explicit parameters that vary in dev-vs-production configurations. Maybe it's looked up from a key that's the local hostname. Perhaps, even, it's looked up based on the 'Host' header, but if the key is absent it's a failure. (Then, the available mappings are a sort of whitelist.)

The official Django recommendation essentially equates to, "be sure to enforce a whitelist on passed 'Host' values at the HTTP server". So it's leaving responsibility to the many alternate web server configurations Django devs might be using... while it could be solved definitively with a slightly different practice inside Django itself.

[jacobian]

It's a tough line to draw. Requiring users to whitelist every domain that might be used to access the app is a PITA, and makes the lives of new developers more annoying. (It also makes multi-tennancy by domain name, e.g. customer.example.com, a bit more difficult.)

On the other hand, you're completely right that the "you gotta get your upstream server configured correctly" advice is handwavy at best.

Seems like this is always the case, this tension between security and usability...

If you've got bright ideas, I'd love to hear 'em. Maybe join us on django-dev (http://groups.google.com/group/django-developers) if you do?

[eli]

I can't totally disagree, but "enforcing a whitelist on the server" is not exactly a tall order. It's the default for many installs and IMHO is already a clear best practice for a production web server. Having your site available under hostnames you didn't intend to make public is generally not a good idea -- it runs the risk of Google picking the wrong one as canonical for one thing.