Windows XP End-of-Life Could Cripple PCI Compliance

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A 403 Labs QSA, PCI Columnist Walt Conway has worked in payments and technology for more than 30 years, 10 of them with Visa.

PCI DSS has two sunsets coming up. The first is the well-documented end of PA-DSS v1.2 this October. The second, and equally significant, sunset is Windows XP's end-of-life just a few months later, and this event may have an even more direct impact on retailers.

The demise of Windows XP will challenge retailers with POS or other payment applications running in that environment. These retailers will fall into one of three scenarios, described below. How they choose to address the situation will affect their PCI compliance and, more importantly, their security. There may even be a little fallout for the PCI Security Standards Council (PCI SSC) itself.

On April 8, 2014, about 14 short months from now, Windows XP will reach the end of its life as an operating system. That means that starting on April 9, 2014, Microsoft (NASDAQ:MSFT) will no longer market, support or provide regular security patches for that operating system. Retailers with POS or other payment systems running on Windows XP after this date will, therefore, no longer be PCI compliant.

Retailers running POS applications on Windows XP must act without delay. According to Microsoft: "If your organization has not started the migration to a modern desktop, you are late."

Why does an end-of-life operating system cause a retailer to be noncompliant? After all, the term "end-of-life" appears nowhere in the PCI DSS. A search of the FAQ on the PCI SSC's Web site also turns up nothing.

Merchants cannot continue to use a payment application based on an end-of-life operating system, because that end-of-life condition runs up against PCI DSS Requirement 6.1. This requirement states merchants must: "Ensure that all system components and software are protected from known vulnerabilities by having the latest vendor-supplied security patches installed. Install critical security patches within one month of release." Once an operating system (or an application) goes past its end-of-life, the vendor does not keep an eye out for new vulnerabilities or release any new security patches.

In addition, and aside from PCI DSS compliance issues, retailers with end-of-life operating systems put themselves squarely in every hacker's cardholder data breach bulls-eye. The bad guys scan merchants' networks for weaknesses, and an end-of-life operating system may be an open invitation for them to do their worst—particularly when unpatched vulnerabilities are spotted.

Retailers with Windows XP POS or payment applications likely will fall into one of the following scenarios.

Scenario 1: "We are OK; we can migrate to my vendor's PA-DSS validated versions for, say, Windows 7 or Windows 8." To confirm this situation, retailers must check the PCI SSC's list of PA-DSS validated applications. Look under the "Tested Platforms/Operating Systems" part of the table to see what options are available.

A quick check of the PA-DSS list showed many applications that run on Windows XP also have alternate validated versions available. Some questions for retailers in this scenario are: How difficult will it be to change operating systems? What other systems in the payment environment are affected? How long will it take? Do we have the internal resources and expertise for a seamless migration? What will upgrading the application cost?

Scenario 2: "We think we'll be OK; my vendor said they will have new version in time." It is true that some applications can simply be installed and run on a newer operating system, but the ability to function in another operating system is not enough. Each application's PA-DSS validation must include testing for every platform. This means a vendor that had its application tested only on Windows XP needs a new assessment to test that application on, say, Windows 7.

My check of the PA-DSS list uncovered a number of validated applications with only Windows XP versions listed under Tested Platforms/Operating Systems. Therefore, although it may sound reassuring to hear that your old Windows XP POS can (possibly) run on Windows 7 or Windows 8, that fact alone is no guarantee that the version is or will be PA-DSS validated. Some questions for retailers in this scenario are: What are the vendor's plans for PA-DSS validation? Can we see something in writing? Is the PA-QSA engaged or scheduled yet? How soon can we see the Implementation Guide, so we know what we are in for? How much will this cost?

Scenario 3: "We don't know the impact yet, because we have a complicated POS environment." Scenario 3: "We don't know the impact yet, because we have a complicated POS environment." This group includes any retailer with self-serve kiosks, gasoline pumps or similar environments that run on Windows XP. These kiosks can involve multiple interfaces that connect payment acceptance, receipt printing, product delivery robots (e.g., in a vending machine), display screens and Internet access. That means changing the operating system may be a complicated project. This group of retailers also includes franchisors with a large number of different franchisee environments, where changing an operating system could be far from trivial.

The questions for these retailers include all of those listed in scenarios 1 and 2.

Could retailers just keep their end-of-life Windows XP operating system and develop a compensating control for Requirement 6.1? That approach could be difficult. Retailers are not likely to have either the resources or access to the Windows XP source code to identify new vulnerabilities or to develop their own security patches and then push those patches to the affected Windows XP systems with the same rigor and robustness as the vendor that developed the product originally.

Developing a compensating control would be difficult, because every compensating control requires a risk analysis. In this case, the control would need to reflect a high likelihood of a maximally damaging system compromise. Conceivably, a retailer could combine a host-based intrusion protection system (IPS) with enhanced monitoring and, say, frequent penetration testing. But what is the rationale for needing the compensating control in the first place?

A compensating control is designed for situations where the merchant "cannot meet a requirement explicitly as stated, due to legitimate technical or documented business constraints." Although merchants have a fair amount of leeway in defining these "constraints," both the advance notice of Windows XP's end-of-life status and the number of operating system (and payment application) options argue against this being an easy case to make. Another reality is that any compensating control is only good until the next assessment, which usually is one year. Retailers contemplating this path need to work closely with their QSA and their acquirer before pursuing any type of compensating control strategy.

Windows XP's upcoming end-of-life may have a subtle impact on the PCI SSC's list of validated applications. Normally, a PA-DSS validation on a given application version and platform is good for three years, after which a new report on validation (ROV) must be prepared and submitted to the PCI SSC for review and acceptance. Will the PCI SSC accept ROVs for Windows XP payment applications this fall (some of these were originally validated under the expiring PA-DSS version 1.2) for the full three years? A 2016 renewal date would be almost two years past the operating system's end-of-life date. Similarly, what about currently listed Windows XP-based applications with 2016 expiry dates? I noticed several of these in my pass through the list. Would—or should—the PCI SSC revoke its validation on April 9, 2014, even though there would be two years left on the original validation?

Having raised this question, let me now knock it down. Regardless of an application's PA-DSS status, if the application is validated and running on an end-of-life operating system, it will not be compliant with PCI DSS Requirement 6.1 and the retailer is not PCI compliant. The fact that the Windows XP version is PA-DSS validated is a technical detail that does not change the facts on the ground.

Do you have Windows XP POS or payment applications? What are your plans for migrating away from Windows XP in the coming year? Or, do you just plan to head to Tatooine and watch both sunsets? I'd like to hear your thoughts. Either leave a comment or E-mail me.