Thoughts On Avoiding The Complex POS Attacks

I have been watching the Target breach story unfold with great interest. In full disclosure, I have no insight into what has happened at Target, beyond the reports that are publicly available. What follows is purely hypothesis and speculation for the purposes of identifying potential mitigations for what may have happened.

Clearly, we don’t know the precise details of how the attack was carried out, however there has been a lot of analysis of various aspects of what is known, including this report from SecureWorks. Malcovery has also released a report speculating the method of entry based on the file hashes provided by in an earlier report by iSight. I am most interested in identifying how the attack happened and what can be done to defend against such an attack. The SecureWorks report provides a good high level list of activities, but not a lot of specificity. For example:

– Firewall ACLs — Access control lists (ACLs) at network borders can be an effective short-term mitigation technique against specific hosts during an active incident when response policies dictate that network traffic to a hostile host be terminated.
– Network segmentation — Organizations should segment PCI networks to restrict access to only authorized users and services.

Among many others are great concepts. However, my observation is that these are not deterministic states, rather they are subjective. What is an “authorized user or service”?

Malcovery believes that the Target attack likely began with a web server being compromised with an SQL injection attack. Let’s assume this is true for a moment in my hypothetical retailer MaliciousCo (oddly, the victim). My web server is on a dedicated network segment. But my site is, of course, a web app connected to a database server. My web site needs to connect to my SQL server, but I don’t want my SQL server hanging out on a network that is accessible to the Internet, even if I don’t allow Internet-originated traffic to the SQL server itself, so I put it on an internal network, because I have other business applications and processes that need to access that same database server. Now, I have a legitimate case where my web site and SQL server are authorized to talk to one another. Because I am a diligent architect, I even route the traffic between the web and SQL servers through an IPS. However, I have created a path into my organization from my web server to my internal systems.

One of the first lessons here, assuming this is the case, is that there should not be ANY connectivity between external server networks and internal networks. The one caveat I would extend is to allow INBOUND traffic from limited internal hosts and the external networks. Outbound traffic into internal networks is not permitted. Not for SQL, not for active directory, not for anything. Additionally, outbound traffic to the Internet should be blocked from hosts on Internet accessible networks too. Only allowing inbound connections from the Internet. The exception might be a very specific mechanism for accessing a payment gateway.

Having done this, any intrusion into my web server is contained on the server itself, along with any other systems that might be on that same network, and there is no practical avenue of lateral movement into the innards of my MaliciousCo network.

Interestingly, in the case of Target, I doubt very highly that the problem involved the main web environment, which includes their online retail operation. We know that the breach didn’t involve the online part of Target’s business. We have also heard Target make reference to a vendor’s credentials being used to commit the breach. At this point, it’s not at all clear exactly what they meant, but I theorize Target is referring to the BMC Patrol user ID and password seen hard coded in the POS malware. However, this opens up another line of consideration: extranets or vendor portals. I have no insight into whether Target actually has such a thing, but my hypothetical mega retailer MaliciousCo does. This vendor portal is used by vendors to receive orders, submit invoices, communicate shipment information and so on. This portal is wholly separate from my main web presence. Access to the vendor portal is obtained via an authenticated VPN and isn’t accessible to the Internet at large.

If one of my suppliers becomes compromised, an attacker might have access to my vendor portal. Since I don’t have any direct control, or even indirect control over my vendor’s security posture (yes, I have them complete a checklist once per year, but we both know this is a Kabuki dance), I opt to treat the vendor portal exactly as I do my Internet sites by isolating them. This effectively restricts the ability of an attacker controlling my vendor portal from lateral movement into my network.

Having said all of this, we don’t actually know how Target was breached. We know that a number of major breaches in the past have happened as a result of SQL injection on web servers. But, it’s also possible that the initial attack looked like Syrian Electronic Army attack, relying on iteratively more sophisticated and deeper spear phishing attacks. Or, maybe it perpetrated using a watering hole attack using a site of interest to the retail industry – after all, we are hearing that there are many retailers involved. Or maybe it’s an attack on Cold Fusion running somewhere in their environment. My point is that there are many windows of opportunity. If MaliciousCo does a stellar job of isolating the web environment, determined attackers are going to try another approach to get at my juicy POS terminals.

My POS terminals should be on a strictly isolated network with all required Supporting infrastructure contained on that network. The only exception being specific access to a payment gateway.

Planning for failure of other controls, my POS terminals themselves should be well locked down, using application white listing to block execution of any unknown software.

Configuring and isolating environments like this is inefficient, cumbersome and expensive. Our adversaries are clever and highly motivated. I am not proposing that we have to take these drastic and costly precautions; we can continue to optimize the design and operation of our IT environments around the axis of efficiency, but we should not feign surprise when major breaches occur. Breaches are inevitable where we have the intersection of means, opportunity and incentives. We can’t do a lot about the means or incentives variables. But we do control the opportunity variable.

I’ll be following up with a few more posts about different aspects we can learn from such as monitoring later.

By the way, I am not proposing that I have the only answer to this. This is a thought experiment and I encourage you to post your views, ideas or criticisms in the comments.

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