Security Concerns about the nsca daemon

[Marc Haber]

On Tue, Feb 21, 2006 at 01:48:14AM +0100, Andreas Ericsson wrote:
> Marc Haber wrote:
> >I'm having a headache about using nsca to receive passive service
> >checks. My concern is possible bugs which could lead to a local user
> >compromise on the nagios host, which in turn could be escalated to
> >root privileges by exploiting one of the numerous kernel bugs that
> >today's Linux systems are plagued with.
> >
> >Since Nagios systems are usually allowed to connect to important
> >systems to be able to conduct active service checks, the nagios host
> >could then be abused to stage attacks against productive services
> >holding valuable data.
> >
> >I would be more comfortable if it would be easily possible to run nsca
> >chrooted. If the chroot is sufficiently minimal, exploting privilege
> >escalation bugs from inside the chroot is significantly harder than if
> >a full system including all binaries would be visible.
> >
> 
> Normally, /var/empty is used. It is supposed to have mode 01700 and be 
> owned by root:root, which means it's as secure as it can get.

The directory to chroot to should be configurable at compile time to
help FHS-compliant distributions. On Debian, the directory to use
would be /var/run/nsca, by example of sshd.

> >I am dreaming of an option which would make nsca chroot itself after
> >starting up like bind9 does. This greatly decreases the number of
> >files that need to be visible in the chroot, but nsca would need to be
> >started with root privileges to allow it to chroot itself. It would
> >then need to drop privileges after chrooting itself. The code needed
> >to do so can probably be pulled from bind.
> >
> 
> I've got a nifty snippet that does this in a secure fashion that also 
> prevents chroot jail breakouts (which bind had troubles with at first). 
> I'm not sure how portable it is though, but for the nsca daemon that 
> shouldn't be extremely important.

It would be great to have that patched into nsca. Portability issues
can be detemined and worked out by use of the Debian buildd network
and the experimental distribution. Since both sean and me are members
of the Debian Nagios team, Debian infrastructure is available for this
effort.

> >For the interface to nagios, it would be extremely handy if the nagios
> >daemon would be able to establish more than one named pipe as a
> >command file. In that case, one could place one extra named pipe
> >inside the nsca chroot, allowing nsca and nagios to communicate
> >without any extra scripting effort.
> >
> 
> This is trickier. Currently, FIFO is emptied continuously in a separate 
> thread that *only* polls the socket. Creating another thread to check 
> one more FIFO is not a good idea, as lots of code need to be made 
> reentrant (i.e. they need to be capable of safely executing in several 
> threads at one time).

And they're hard to make reentrant?

> Another option is to make the current thread 
> multiplex several FIFO's, but that too is a far from simple solution.

Sean has pointed out a way to do this which doesn't look that
complicated.

> Fortunately, it's also completely unnecessary. A process can open(2) a 
> file, FIFO or socket prior to doing a chroot and then write(2) to it 
> from the chroot jail, even though the file (or FIFO, or socket) doesn't 
> reside anywhere below that path.

As sean has already said, this breaks as soon as the nagios daemon
re-creates the named pipe for some reason.

> >Unfortunately, I do not have the coding expertise to submit a patch.
> >
> >I would therefore like to see my suggestion discussed - maybe I am
> >completely misled. Any comments will be greatly appreciated.
> >
> 
> I do, and this suggestion is a good one. I'll see what I can do, 
> although I'm fairly drowning in work at the moment (as usual).

If I can help in any way, please say so.

Greetings
Marc

-- 
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Marc Haber         | "I don't trust Computers. They | Mailadresse im Header
Mannheim, Germany  |  lose things."    Winona Ryder | Fon: *49 621 72739834
Nordisch by Nature |  How to make an American Quilt | Fax: *49 621 72739835


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