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Comment by jcalvinowens

17 hours ago

I doubt it: aslr is not as easy to break on modern Linux as everyone in this thread wants to pretend it is. And anybody who actually cares so much about security that a compromised web frontend is the end of the world should be doing other things which would additionally mitigate this...

I know they claimed they can bypass it: if that's true, they should publish it. The forking nature of nginx is uniquely bizarre and vulnerable, and I strongly suspect that's the only way they're pulling it off. I feel like that's the interesting thing here, not the buffer overrun.

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jcalvinowens

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linkregister  14 hours ago

Apache used forked processes; I don't think that's unique or a particular issue. NGINX uses async io to handle requests, which is a substantial upgrade from Apache; that's why it's performant.

Memory corruption vulnerabilities are possible whenever a language is used that performs copies of data across buffers without in-language guards.

This vulnerability does not require knowledge of the memory layout to generate worker crashes against a system with vulnerable configurations.

The vulnerability is not the end of the world. System administrators will upgrade nginx with the security patch when it's released across most distribution paths (right now it's available only on unstable Debian for example). In the meantime sysadmins will likely remove the vulnerable directives from nginx configs.

  • cestith  1 hour ago

    Apache actually has had multiple modules for its concurrency for many years. The event and worker multi-processing modules use threading rather than forking.

  • jcalvinowens  12 hours ago

    > Apache used forked processes; I don't think that's unique or a particular issue.

    Of course it is... in a typical threaded daemon, the threads have randomized stack addresses. Exactly as you observed, you get unlimited tries because nginx dutifully restarts the worker process with the same literal stack address every time it segfaults. I'm willing to bet the ASLR break they claim to have relies on that, but I'd be happy to be proven wrong if they publish it :)