Archive for March, 2013

24
Mar
13

Why vSkimmer Should Not Matter

It was announced this week by McAfee that a new threat to merchants has been discovered called vSkimmer.  This is a very insidious threat as most merchants will likely not know they have been infected until it is too late.

The net of vSkimmer is that it is malware of the highest order built for the explicit purpose of collecting track 2 data from Windows point of sale (POS) systems.  Worse yet, whoever wrote this little gem of software intends to enhance it in 2013 to include the ability to skim EMV cards’ “track” data as well.

vSkimmer can be deployed like Stuxnet through a USB thumb drive, as malware in an email message or on a Web site or any number of ways.  When installed, vSkimmer determines the operating system and version, hostname, active username and various other operational characteristics of the POS system.  It then inventories running tasks and memory to determine where track 2 data is stored and begins recording that data.

vSkimmer works whether the POS system is connected to the Internet or not.  When the POS is connected to the Internet, it transmits the data obtained to a control server using HTTP.  When the POS is not connected to the Internet, the information is stored until someone connects a USB device labeled ‘KARTOXA007’ and copies all the information it obtained onto the USB device.

As usual, the Internet is abuzz regarding how this will be addressed by the PCI DSS.  Sorry to disappoint, but it is already addressed.  Here are some key requirements in the PCI DSS that should mitigate vSkimmer.

  • Requirement 1.2.1.a requires that only that network traffic that is necessary is allowed through the firewall.  Merchants should be only allowing connectivity from the POS or card terminal to their processor and nowhere else.  Any traffic attempting to go anywhere else should be flagged and IT alerted to investigate.
  • Requirement 5.1 requires that you have anti-virus and anti-malware software installed on POS devices.  Given this is a Windows specific threat and Windows is highly susceptible to being infected, you should have done this already.  While anti-virus solutions are not perfect in always identifying such malware, since McAfee and other anti-virus solution vendors are the ones that found vSkimmer, I would imagine that they all have or will very soon have signatures for vSkimmer.
  • Requirement 6.1 requires that systems are patched current.  The problem with patching POS systems is that a lot of vendors issue POS updates for the OS and their application on a quarterly or even annual basis and do not recommend that merchants patch their POS systems directly from Microsoft because of compatibility issues.
  • Requirement 10.2 which requires the logging of events.  In the case of a USB device being plugged into the POS system, at a minimum you should see that the portable device enumerator service going active when a USB device is plugged in and if the device is new, you should see system event log entries regarding the loading of device drivers to support the USB device.  None of these actions should be seen in your log data, so if you monitor for these events, you will know that USB devices are potentially being plugged into your POS systems.
  • Requirement 10.5.5 requires the use of file integrity monitoring which would catch the installation of vSkimmer as a foreign piece of software even though it masks itself as ‘svchost.exe’.  This would provide a backup control for requirement 5.1 if vSkimmer changes its approach as to its file name and is not caught by the anti-virus solution.

In addition to the PCI requirements, you can do the following to increase your security in regards to vSkimmer.

  • Do not allow USB devices to be connected to your POS systems.  Most card terminals are RS232 devices, but USB is becoming more common.  The Windows Group Policy function can be used to disable USB ports on Windows systems.  There are also third party solutions that will disable USB ports.  A lot of these third party solutions can offer additional granularity in what types of USB devices can be connected.  This can be very advantageous when you are using USB card terminals which still need to connect, but other USB devices should not be allowed.  One of my more imaginative clients hot glues the ports shut on their POS systems.
  • Train your staff on the vSkimmer threat.  Explain how it works and what they can do to minimize this threat such as not allowing anyone to manipulate the POS systems other than employees responsible for the care and maintenance of the systems.
  • Lock your POS systems in a sealed cabinet or cage and only allow the manager on duty to have the key.  This may also involve additional security on POS servers if those are also used by your POS solution.
  • Periodically review video of your POS stations to determine if cashiers or other personnel appear to be manipulating the POS system.

If you adopt all of these measures, you will significantly reduce the threat presented by vSkimmer and will likely never encounter it.

07
Mar
13

Encrypted Cardholder Data – Out Of Scope?

I had an interesting exchange on Google+ the other day regarding whether or not encrypted data is in scope for PCI compliance.  In the end it was suggested that I write a blog entry regarding this topic as they said how to treat encryption has not been articulated very clearly by the PCI SSC.  I would argue that the rules regarding encryption and scope have been very clearly articulated in the PCI SSC’s FAQ #1086.  However, based on the conversation we had, it was obvious that this is not the case.  So here are the rules as practiced by most QSAs.

The key to how to interpret whether or not encrypted cardholder data is in-scope is in the FAQ.  Encrypted cardholder data (stored or transmitted) being out of scope is based on whether or not that data meets the following definition.

“It is possible that encrypted data may potentially be out of scope for a particular entity if, and only if, it is validated (for example, by a QSA or ISA) that the entity in possession of the encrypted data does not have access to the cleartext cardholder data or the encryption process, nor do they have the ability to decrypt the encrypted data.”

The important phrase in the aforementioned definition is “if, and only if.”  The only way encrypted cardholder data (CHD) is out of scope is if the entity being assessed for PCI compliance cannot decrypt the encrypted CHD.  This is a very important concept that gets constantly misinterpreted by QSAs and their clients.  However, it is up to the QSA to confirm that the organization being assessed cannot decrypt the encrypted CHD and to document the procedures conducted to prove that fact.

With that as background, let us look at storing and transmitting encrypted data and how they can be out of scope and what that means.  As you will see, out of scope can mean different things depending on the implementation of encryption.

Stored Cardholder Data

Under requirement 3.4, one of the methods recommended for the storing of the primary account number (PAN) is:

“Strong cryptography with associated key-management processes and procedures“

One of the ways organizations accomplish this is through a hardware security module (HSM) that manages the cryptographic key process.  The HSM generates the keys, manages the keys and provides an application programming interface (API) for code to access the keys.  Since the HSM is a “black box” a lot of organizations point to that fact as the reason their encryption is out of scope.

There is an additional condition to the encryption out of scope definition that usually gets forgotten.  This is what allows for the scope of the cardholder data environment (CDE) to be reduced.

“Systems performing encryption and/or decryption of cardholder data, and any systems performing key management functions, are always in scope for PCI DSS. Scope reduction for encrypted data may only be considered when that data is isolated from these processes.”

As such, since the organization using the HSM technically has access to the cryptographic keys through the HSM’s APIs, the encryption is in-scope.

Where stored encrypted CHD is out of scope is when a third party controls the encryption keys.  This most often occurs with tokenization.  Under a tokenization scheme, the CHD is sent to a third party who then securely stores the CHD and returns a token that links the CHD at the third party to the token stored by the merchant.  If the merchant needs to make any subsequent charges to the account, the merchant sends the stored token to the third party and the third party substitutes the stored CHD for the token and the transaction is completed.  But since the merchant does not have access to the token creation process, the token is out of scope because it is no longer considered CHD.

Transmitted Cardholder Data

Secure transmission of CHD can be accomplished through a number of methods.  The most common of these methods is secure sockets layer (SSL) or transport layer security (TLS).  In either case, if the organization being assessed has one of the endpoints in the SSL/TLS encryption, then the SSL/TLS process is in scope.  This is obviously most common in the conduct of e-Commerce when the merchant’s Web site has an SSL/TLS certificate for securing the transmission of the CHD to pay for the customer’s purchases from the Web site.

However we are also seeing SSL/TLS used more and more as the encryption method of choice for point-to-point encryption (P2PE) solutions.  Again, if either of the endpoints in the P2PE environment are under the control of the organization being assessed, then the endpoint or endpoints are in-scope for the PCI assessment.

One way we do see to get everything but the merchant’s endpoint out of scope is terminals that are encrypted from the terminal to the processor and the processor controls the encryption keys for the P2PE.  This is most often used in the gas station environment where the pump card reader does P2PE to the processor using derived unique key per transaction (DUKPT) or similar techniques to create an encrypted connection.

That said, what happens to the users and devices in between the two encryption endpoints on an encrypted communication link?  They are out of scope as long as they do not have the ability to decrypt the data stream.  This is another misunderstood interpretation of the FAQ.  While some personnel inside an organization have access to encryption keys, if a user or device does not have access to the encryption keys or the communication endpoints, they too are out of scope.  This is how an SSL/TLS/IPsec connection can be used for isolating the transmission of CHD from the rest of the network and satisfy network segmentation.

Another issue that comes up with managed service providers (MSP) is when the MSP has access to firewalls or routers that are encryption endpoints.  Even if the MSP does not have access to the encryption keys, they do have access to the encryption endpoint(s) and cleartext CHD, therefore their personnel and relevant device management practices are in-scope for PCI compliance.

The bottom line in all of this is; if your organization has the ability to decrypt either the stored CHD or transmissions of CHD, then you are in-scope for PCI compliance.

And as a reminder to everyone, just because something is out of scope it does not mean that it does not need to be assessed.  It is always necessary for a certain amount of testing procedures to be conducted to determine that the item is out of scope.

Hopefully we can now all operate from the same set of rules.




March 2013
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