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Thursday, 20 July 2017 08:28

CyberArk finds new way of domain fronting for use in attacks

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Researchers from the Red Team at CyberArk Labs have found a new way of domain fronting that allows an attacker to mask malware command-and-control traffic and abuse content delivery networks like Akamai.

Shay Nahari, who heads the Red Team at CyberArk, said in a blog post that domain fronting had been used before in the wild by experienced attackers as an evasion technique.

Nahari told iTWire that the company had identified tens of thousands of domains served by Akamai's content delivery network that could be used for domain fronting. These included Fortune 100 domains and could be used in targeted attacks.

According to a research paper, domain fronting uses different domain names at different layers of communication. In an HTTPS request, the destination domain appears in the DNS query, the TLS server name indication extension and the HTTP host header.

In an ordinary request, the same domain name appears in all three places. In a domain-fronted request, the DNS and SNI carry one name - a kosher one - while the HTTP host header, which is hidden by host encryption, carries another.

The frontend server would direct the request to the domain specified by the host header and no traffic would go to the domain specified by the other two parameters.

Nahari said that for the CyberArk method to be used, one needed a content delivery network that hosted a two-way persistent read-write system or application.

"For example, in our testing, our malware utilised the API of a commercial to-do list application hosted by the content delivery network to exchange instructions and data with us," he said.

Also needed was malware that had been specially written to use this command-and-control channel; it needed to be implanted on users' machines.

Nahari said multiple third parties' API sharing the same edge network were first identified within the content delivery network, and multiple persistent lists of commands were created using the shared API interface. These lists acted as the malware command queue. Different lists were utilised by the malware and the server to issue commands and receive output.

Custom malware was then created to use token data and the content delivery network customer's API to read and write requests to the command-and-control system.

From the perspective of the defender, the client machine would be sending a request to a reputed domain and the traffic would be encrypted and signed by this domain, he said.

One way of mitigating this method of attack was for organisations to monitor and control traffic leaving their networks, Nahari said.

"One theoretical solution is for the content delivery network to associate virtual IP addresses with each domain, which can be assigned to a specific SSL certificate and therefore protect against the cross-tenant approach we’ve demonstrated," he said.

"There are, of course, practical limitations to this approach, perhaps most importantly the shortage of public IPv4 addresses."

Nahari said while Akamai's was not the only content delivery network that was susceptible to this technique, the fact that it handled so much Internet traffic made it a juicy target.

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Sam Varghese

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Sam Varghese has been writing for iTWire since 2006, a year after the site came into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.

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