[syslog-ng] Controlling Logging to Central Syslog-ng Server, DoS etc

Balazs Scheidler bazsi at balabit.hu
Fri Oct 6 13:54:06 CEST 2006

On Fri, 2006-09-22 at 16:34 +0100, Hari Sekhon wrote:
> nate wrote: 
> > On Fri, Sep 22, 2006 at 03:18:50PM +0100, Hari Sekhon wrote:
> >   
> > > After all, you couldn't somebody just write a loop to send garbage to it 
> > > and fill the whole machine up, not to mention drown out all other valid 
> > > logs so you miss any important events (oops, I am giving away too much 
> > > here?). I'm actually tempted to write an attack for this right now...
> > >     
> > 
> > This is always a risk. It's obvious enough that it's not discussed much.
> > syslog-ng has tcp wrappers support, and you always have packet
> > filtering.
> > 
> > You should certainly block unauthorized IPs, but your authorized IPs are
> > just as scary as the others. The miscreant will either be an authorized
> > user or have compromised an authorized account and will flood your
> > syslog server from there.
> > 
> > If you want to dicuss DoS, come up with a way to deal with that.
> >   
> I agree. Unfortunately, the syslog protocol is insecure by nature and
> therefore we are left with either old ip filtering which as you said
> still leaves a problem, in that a miscreant will either be an
> authorized user or have compromised an authorised user's account.
> In fact, it's even worse because you can simply spoof an address of a
> real server to get through. It's even easier if you allow udp because
> they could just fire off udp packets without even having to reply to
> them and therefore you don't even need to take over the ip of the
> spoofed machine.
> One possibility is that you could try and surpass syslog protocol by
> allowing only syslog-ng tcp connections and providing some
> authentication mechanism like certificates or keys or something, like
> ssh keys or some other public private certificate system. Although the
> overhead will be considerable, both in machine terms and humans admin
> terms, but I can't think of any other way of really doing this at the
> moment.
> Perhaps instead of the connection being authenticated, the packets
> themselves could be signed, although I'm no cryptography expert to
> know how secure that would be against forgery.
> Would it be more secure to use a tcp SSL tunnel using  or something
> and then set up tunnels for the syslog machines? Although highly
> secure in that only specific machines could go through to the server
> and loop back in to the syslog server, you'd be left with those
> servers being the only points of failure regarding malicious users or
> compromised accounts, other than the syslog-ng server itself.
> I feel that it would be a huge and difficult task to add serious
> security to syslog-ng beyond this.
> just my 3 cents...

I have already committed partial TLS support to my internal development
tree. If you only allow TCP/TLS connections with X.509 certificate based
authentication, then _if_ you trust complete hosts (e.g. no rogue
users), you should be fine. 

There's also a syslog-sign draft floating around, which signs individual
syslog messages, but that requires even more application support which
currently simply does not exist.


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