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Private encryption key sharing worrying but not new, say security experts

A study has revealed a 40% increase in the past year in the number of internet-connected devices using shared encryption certificates, highlighting that this security risk of mass hacking is growing

The re-use of private encryption keys is worrying, but not new according to security experts responding to the latest report on the issue by security firm SEC Consult.

Around 4.5 million internet-connected devices continue to share known private keys for encrypting their communications, a study has revealed.

One certificate is shared but 500,000 devices, while another is shared by 280,000 devices connected to the internet.

According to the latest study, the number of devices doing so is up by 40% in the past year, when compared with the findings of SEC Consult’s study of hardcoded cryptographic secrets in 2015.  

This is despite the firm’s efforts to inform 50 different suppliers and various internet service providers (ISPs) about devices on the web using known private keys for HTTPS server certificates.

The report cites the inability of suppliers to provide patches for security vulnerabilities, including – but not limited to – legacy or end-of-life products as the most likely reason.

However, even when patches are available, embedded systems are rarely patched, according to SEC Consult.

The firm also cites insufficient firewalling of devices on the wide area network (WAN) side by users and ISPs in case of ISP-supplied customer premises equipment (CPE), and the trend of internet of things-enabled products as other likely contributory factors.

In the spirit of open research, the security firm has released the raw data on Github, which includes 331 certificates including the matching private key as well as 553 individual private keys.

Read more about keys and certificates

The data also includes the names of products that contain the certificates/keys and cryptographic keys that were not found in internet-wide scan data.

The data allows researchers to reproduce the results of our study, find more cases or cryptographic key reuse, attribute cryptographic keys to specific vendors/products, and to develop tools for detecting and exploiting this vulnerability class in the course of penetration tests, SEC Consult said.

The company admits that releasing the private keys allows attackers to exploit this vulnerability on a large scale, but said any determined attacker would repeat the research and get the private keys from publicly available firmware with ease.

SEC Consult is calling on suppliers to make sure that each device uses random, unique cryptographic keys that can be computed in the factory or on first boot.

In the case of CPE devices, both the ISP and the supplier have to work together to provide fixed firmware for affected devices.

ISPs also have to make sure remote access via the WAN port to CPEs is not possible. In case the ISP needs access for remote support purposes, setting up a dedicated management VLAN with no CPE-to-CPE communication is recommended.

Users should change the SSH host keys and X.509 certificates to device-specific ones, SEC Consult said, adding this is not always possible as some products do not allow this configuration to be changed or users do not have permissions to do it.

But SEC Consult said some of the required technical steps are not something that can be expected of a regular home user.

Although re-using private keys in critical network security devices is not new, the findings are disturbing, particularly in the light of the fact many of the affected devices are used in critical infrastructure and telecommunication systems, said Kevin Bocek, vice-president of security strategy and threat intelligence at Venafi.

“We share SEC Consult’s frustration. The use of encryption is meant to uniquely authenticate application and protect privacy, so leaving devices with keys and certificates that are reused hundreds of thousands of times is insane,” he said.

Bocek added that the practice is tantamount to repeatedly leaving the key to kingdom on the doorstep and putting up a billboard to advertising the vulnerability.

“Conventional security – intrusion detection systems, firewalls and antivirus – will not help when an attacker is looking inside your encrypted traffic, or masquerades as one of your trusted applications or devices. Bad guys can literally take whatever data they want undetected,” he said.

According to Bocek, the problem is only going to get worse with millions more devices being added daily.

“DevOps is driving developers to go faster and skills protecting keys and certificates are in short supply. It’s not surprise then to see the problem getting worse. Internet of things devices developed or deployed, and in many cases in DevOps organisations, multiply the problems many times over,” he said.

Venafi believes companies need to take back control and take immediate action to protect themselves.

By identifying all keys and certificates used on networks, across the cloud, and out to the internet, said Bocek, organisations can identify possible failures like rampant key reuse that threatens to smash the foundation of security.

“Once key reuse is identified, organisations can then triage: either replacing with new unique keys and certificates those that can be, or quarantining those that can’t and working with suppliers to resolve,” he said.

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