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Telstra to DNS-block botnet C&Cs with unknown blacklist

What could possibly go wrong other than a C&C net sharing your colo barn's IP address?

Internet Security Threat Report 2014

Telstra is preparing to get proactive with malware, announcing that it will be implementing a DNS-based blocker to prevent customer systems from contact known command-and-control servers.

The “malware suppression” tool will will be introduced at no cost for fixed, mobile and NBN customers using domestic broadband and Telstra Business Broadband services.

The service is using a command-and-control address list sourced from an unnamed Californian partner, and the carrier maintains that it won't be recording users' browsing history.

However, there seems to be a little confusion between different arms of the carrier as to how the malware suppression service works. Here's how the promotional blog post discusses the technology:

“Because the malware suppression technology only observes DNS queries and not internet traffic, no internet search history, browsing data or any other customer data is recorded, retained or sent to a third party.”

(Vulture South notes that the last time we looked, DNS queries travelled over the Internet. We therefore conclude that Telstra is trying to reassure customers that the content of their browsing is not examined.)

In its support Q&A, the carrier states:

“We do not retain a record of legitimate DNS queries made by your computer and those legitimate queries will be unaffected by the new malware suppression” (emphasis added).

As the same page notes, if the carrier has reason to query (sorry) a DNS query, it will fire off a query to California:

“At times, the DNS server may notice a pattern of queries from a number of different users which looks suspicious (for example, why would a real user try to go to a domain like qwe54fggty.dyndns.biz?). In this case, information about the suspicious target domain might be sent to our partner in California to examine whether the domain is a botnet or command & control server.”

However, it states, in requesting that a domain be examined by its blacklist supplier, it will not pass on any information to identify the user or users trying to contact that domain.

In response to The Register's questions, a Telstra spokesperson provided this statement:

"We are introducing malware suppression technology to the Telstra BigPond Network to help improve safety and security of the internet for our customers. We have developed the upgrade to our network with a technology partner, a firm based in the United States. The malware suppression technology does not look at any content our customers are sending or receiving, rather it prevents our customer's computers from being controlled by Command and Control servers. The malware suppression service being deployed on the Telstra BigPond Network works on DNS queries only going to verified Command and Control servers."

Which is likely to be all very well and good, until some poor sap finds their IP address lives on a server also occupied by a C&C server. Such a scenario is not beyond the realms of possibility: in may 2013 Australia's de facto internet filter blocked access to hundreds of sites when the intention was to block just one. Telstra must be hoping its un-named source of C&C systems doesn't make the same mistake. ®

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