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Comment by wutwot | Hacker News Reader

You don't filter out CPP macro's. I would skip that and only allow C code. Or run this thing in a proper jail because at the moment:

- doing an include #include "/dev/random" will block the thread. - including "/etc/passwd" is also possible although I don't see a direct way to turn this into password disclosure.

Seriously; even if it's a weekend project, letting people run all kinds of potentially bad code on your machine is never a good idea. Even though you don't run the binaries yourself there's so many ways to mess around with a compiler. You just don't know what's going to happen.

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chroot would probably be sufficient. Barring some sort of code execution vuln in the compiler you can only load stuff off of the filesystem.

Having the actual CPP available is nice because some bits of libc are only macros.

I have now added some basic macro detection

#define x "/etc/passwd" #include x

I have now fixed it. But I think there must be an other way to make it safe. Maybe a sandbox

This is part of your /etc/shadow file:

    root:censored

We can still read /etc/ssh/ssh_host_rsa_key, etc.

Edit: removed hash, sorry

Saying "you can read /etc/shadow by doing X, Y, and Z" is okay -- it's a permanent record there was a flaw. Saying "here's your root password hash" is not ok; even once the flaw is fixed, that hash is still floating around out there. I'd take advantage of the edit period and remove that from your comment; it's just not cool. The OP should definitely change the root password on the box regardless.

Well one easy way to increase security would for this to stop running as root.

Please, don't ever run your application code as root. Less so when it's facing the Internet.

No problem I think I could fix it.

Can you show us how you read the content of the file. Just want to learn more

If it's a server used for other things, definitely a sandbox. gcc's not exactly security hardend. Best one (novel solution, though the code's old and shit) I've come across: https://pts-mini-gpl.googlecode.com/svn/trunk/uevalrun/doc/u...

I have now used a the wrapper by gcc-explorer https://github.com/mattgodbolt/gcc-explorer/blob/master/c-pr...

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