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RE: Deny access to copy files
From: Craig Wright <Craig.Wright () bdo com au>
Date: Thu, 12 Jun 2008 09:24:04 +1000

If we make the assumption that all configurations, applications and hosts are locked down the same way. From a security 
and risk perspective.

To simplify:
3 hosts with individual CHMOD gaols
        Is better than
3 hosts each with a single app Is comparable to 3 VMs each with a single app in a chmod gaol
        Is better than
3 VMs each with a single app
        Is better than
1 host with 3 Chmod gaols
        Is better than
I host with 3 apps all running together

As for cost, I can get 3 hosts for less than $1500. For a small firm where the issue is not space cooling etc, the cost 
argument is flawed.

" quite possible these days that production systems *will* be virtual"
That is fine as long as the risk is quantified correctly and the appropriate controls are in place. If all systems are 
on the same zone then this is a lessor risk than when people share zones (ie DMZ and production on the same hypervisor 
- and I have seen Gartner present this as well as a host outside the firewall etc).

As the network on a VM is a hub based environment, the issue with separate zones is that information can leak. That is 
internal and external segments can see each other. There are mitigating controls, but these are controls that are not 
necessary on physical servers and also ones that are commonly neglected.

Also remember that the networks with VMs are not switched. This is they are in effect hubs. It is simple to sniff all 
traffic from host to host. Adding separate cards can help, but increases cost.

Have a look at:
        Xensploit - http://www.eecs.umich.edu/techreports/cse/2007/CSE-TR-539-07.pdf
        VM Migration

A quote from the recent Blackhat:
"One of the underlying themes of my presentation is that we've been continually breaking down isolations barriers that 
provide security in exchange for new functionality," Oberheide.

Oberheide noted that systems have moved from physical machines where state is protected by hardware mechanisms such as 
the MMU. Virtual machines protect the machine state in the isolation boundaries of a software layer such as the 
VMM/Hypervisor, ".which, as we've seen, often fails in its isolation," to VM migration where the machine state is 
exposed to the local network. So there are controls that can be added to reduce the risk, but these are additional 
controls not needed on real systems.

Also have a read of:
" An Empirical Study into the Security Exposure to Hosts of Hostile Virtualized Environments" Tavis Ormandy

Some further reading:
T. Shelton, "VMware natd heap overflow", http://lists.grok.org.uk/pipermail/full-disclosure/2005-December/040442.html

G. Delalleau, "Large Memory Management Vulnerabilities", http://cansecwest.com/core05/memory_vulns_delalleau.pdf

Popek, G. J. and Goldberg, R. P. 1974. Formal requirements for virtualizable
third generation architectures. Commun. ACM 17, 7 (Jul. 1974), 412-421

K. Kato, "VMware Backdoor", http://chitchat.at.infoseek.co.jp/vmware/backdoor.html

Craig Wright GSE etc

Craig Wright
Manager, Risk Advisory Services

Direct : +61 2 9286 5497
Craig.Wright () bdo com au
+61 417 683 914

BDO Kendalls (NSW-VIC) Pty. Ltd.
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-----Original Message-----

From: Al MailingList [mailto:alpal.mailinglist () gmail com]
Sent: Thursday, 12 June 2008 12:56 AM
To: Craig Wright
Cc: security-basics () securityfocus com
Subject: Re: Deny access to copy files


But to prove the negative (and to paraphrase a little from the Burton group).
3. Separation reduces risk. Running several systems on the same hypervisor makes them more (not less vulnerable). All 
of the systems are just as vulnerable as a locked down host on a system with the added benefit of also having the 
risk from the hypervisor abstracted onto them.


Ignoring the discussion about development boxes for a moment... I'm a
bit confused at what you're getting at here - I thought in law 3 the
article was alluding to the fact that using VMs as separation *was* a
good idea to offset increased risk from the hypervisor? Quoting the

"One of the ways to benefit from virtualization is to separate various
functions into their own isolated operating environments. An even
better way is to separate data as well. Either type of separation
provides an opportunity to reduce the risk added by the virtualization

As Greg pointed out, non VMware solution in the case a client only
wants to buy a single physical box:
- Mail Server
- Name Server
- Web Server

obviously a large attack surface, and in the event a single service is
compromised, there go the other two services and associated data.
Obviously (I think? :) ) chroot and priv separation is a good idea
here. A different way of implementing separation is of course

Single box
    - Mail
    - Name
    - Web

As you point out, the attack surface is now slightly bigger per
service (if you +hypervisor), but in general two compromises are now
required to compromise all three services (exploit against one of the
services and then compromise of priv separation mechanism (chroot or

Have I missed something? Are you also suggesting chrooting services is
bad idea? I agree with your statement about cost reduction - if cost
doesn't factor into the equation, then by far the best choice is a
physically separate box per service. But can you not also then argue
that with certain constraints placed on the scenario (i.e. I can
afford one physical box), separation does reduce resultant risk (by
reducing severity of a compromise)?

Just a final note out of curiosity, you state:

"Risk = hypervisor_risk + Host_risk"

(which I understand...), but I was wondering, do you have an example
of a vulnerability that would affect virtual machine for an internet
based service? I mean I know vulnerabilities like CVE-2008-1340 are
serious, but obviously they don't increase the initial risk of, say,
an email server being compromised. Examples being a powerful thing, I
was curious in the scenario I presented above (3 vms... 1 runs mail, 1
runs name server, and one runs web) if you could point me at a CVE
that would demonstrate the +hypervisor_risk ?


PS Agreed: internal systems *should* mirror production - it's quite
possible these days that production systems *will* be virtual :D
aced on th??st??

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