Patching the Perpetual MD5 Vulnerability

October 17, 2013

By Gavin Hill, Director, Product Marketing & Threat Research Center at Venafi

Earlier this month, Microsoft updated the security advisory that deprecates the use of MD5 hash algorithms for certificates issued by certification authorities (CA) in the Microsoft root certificate program. The patch has been released so that administrators can test its impact before a Microsoft Update on February 11, 2014 enforces the deprecation. This is an important move in the fight against the cyber-criminal activity that abuses the trust established by cryptographic assets like keys and certificates.

For over 17 years, cryptographers have been recommending against the use of MD5. MD5 is considered weak and insecure; an attacker can easily use an MD5 collision to forge valid digital certificates. The most well-known example of this type of attack is when attackers forged a Microsoft Windows code-signing certificate and used it to sign the Flame malware. Although the move to deprecate weak algorithms like MD5 is most certainly a step in the right direction, there still are some questions that need to be addressed.

Why is the Microsoft update important?

Cryptographers have been recommending the use of hash algorithms other than MD5 since 1996, yet Flame malware was still successful in 2012. This demonstrates that security professionals have failed to identify a vulnerability in their security strategy. However, cyber-criminals have most certainly not missed the opportunity to use cryptographic keys and digital certificates as a new way into enterprise networks. That Microsoft will soon enforce the deprecation of MD5 indicates that vendors and security professionals are starting to take note of keys and certificates as an attack vector.

Research performed by Venafi reveals that 39% of hash algorithms used by global 2000 organizations are still MD5. Such widespread use is worrying on a number of different levels as it clearly highlights that organizations either do not understand the ramifications of using weak algorithms like MD5 or that they simply have no idea that MD5 is being used in the first place. Research from the Ponemon Institute provides evidence that organizations simply don’t know that MD5 is being used—how could they when more than half of them don’t even know how many keys and certificates are in use within their networks?

What’s the impact of the security update?

Microsoft’s update is not to be taken lightly; this is probably why Microsoft has given organizations six months to test the patch. Once they have deployed the update, administrators will be able to monitor their environments for weak cryptography and take action to protect themselves from the vulnerabilities associated with MD5 hash algorithms or inadequate key sizes. Options available to administrators include the ability to block cryptographic algorithms that override operating system settings.

However, if a business has critical certificates that use MD5, enforcing such a security policy could result in system outages that may impact the business’s ability to service customer requests. For this reason, the update allows administrators to choose whether to opt-in or opt-out of each policy independently as well as to log access attempts by certificates with weak algorithms but to take no action to protect the system. The update also allows policies to be set based on certificate type such as all certificates, SSL certificates, code-signing certificates, or time stamping certificates.

Although I understand that Microsoft is allowing customers to choose how wide a net they are able to cast on MD5, the choices system administrators have when a security event is triggered should be of concern. Instead of choosing to apply the security policy to “all certificates,” some companies, out of concern for system outages, may limit the enforcement to a subset of certificate types. After all, history has shown that organizations have neglected to do anything about the known MD5 vulnerability for many years; they might easily continue to postpone the requisite changes. As a result, some companies may leave a massive open door for cyber-criminals to exploit.

Are there other weaknesses in cryptography that should concern me?

MD5 is not the only vulnerability to cryptography that should concern IT security professionals—there are many. However, I am only going to focus on a few of the most common.

Insufficient key length: Since 2011 the National Institute of Standards and Technology (NIST) has deprecated encryption keys of 1024 bits or less. After December 31, 2013, the use of 1024-bit keys will be disallowed due to their insecurity. Despite this, as surveyed by Venafi, 66% of the encryption keys still used by global 2000 organizations are 1024-bit keys. Vendors and service providers like Google, Microsoft, and PayPal made the shift to 2048-bit keys earlier this year. If you have 1024-bit keys in use, now is the time to upgrade to 2048-bit keys.

Lack of visibility: The majority of organizations lack visibility into or understanding of their key and certificate population. Organizations simply don’t know how many keys and certificates are in use on the network, what access they provide to critical systems, who has access to them, or how they are used. Businesses without visibility into such a critical attack vector—and with limited or no ability to respond quickly—are an attacker’s dream. To mitigate against these vulnerabilities, you must gain a complete understanding of your key and certificate population so that you know where your organization is vulnerable.

Inability to remediate: How can you defend something if you don’t know what you are defending? The lack of visibility has led to real vulnerabilities. Forrester Research found that 44% of organizations have already experienced an attack based on keys and certificates. Moreover, 60% of these businesses could not respond to the attacks, whether on SSH or SSL, within 24 hours. And the response, when unrolled, usually involves a laborious manual process that often leaves some systems unchecked.

What can I do to avoid these vulnerabilities?

To protect your business against attacks on keys and certificates, I recommend that you invest wisely in technologies that apply robust policies against the use of weak algorithms and poorly configured cryptography. At the same time, the technology should be able to detect anomalous behavior of keys and certificates and automatically respond, remediating any key—and certificate-based risks.

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