A DNS sinkhole campaign is underway and in high gear to block computers infected with CryptoLocker from reaching the malware's Command & Control servers. A DNS sinkhole is a method used by security researchers to monitor Botnets and to block communication between an infected computer and its Command & Control server. This method is now being used against CryptoLocker, a file encrypting ransomware that requires a $300 USD ransom from victims in order to get their files back. We have been monitoring and helping CryptoLocker victims since its release in early September. This infection has been devastating for its victims.
For quite a while, we have noticed that an unknown organization has started redirecting, or sinkholing, CryptoLocker domains to sinkdns.org hostnames. When CryptoLocker attempts to communicate with certain domains it will instead be sent to a server hosted in the sinkdns.org domain. The connection will also contain the http headers Server: You got served! and X-Sinkhole: malware cryptolocker sinkhole. By sinkholing the domains, communication between an infected computer and the malware's Command & Control server is not able to take place. If CryptoLocker is unable to communicate with a C&C server and receive a public key used to encrypt files, it will endlessly loop till it can. By breaking this communication, security researchers aim to halt CryptoLocker before it further encrypts other infected computer's files.