Law enforcement agencies around the world are mounting an increased effort against cyber criminals, but they don’t seem to get very far. Two recent reports explain why: Gangs are using technology to rapidly and regularly change Internet addresses.
Security reporter Brian Krebs writes today of a botnet of hacked computers around the world that is effectively a criminal cloud hosting environment for a wide range of activity including hosting stolen credit card shops.
Tipped off by security vendor RiskAnalytics, the system changes the Internet address, or domain name server (DNS) of each Web site roughly every three minutes. In a test Krebs did of one site, in a 12-hour period the DNS of one site spat out more than 1,000 unique addresses.
Krebs quotes a RiskAnalytics official estimates there are over 2,000 infected endpoints, mostly in Europe, behind the botnet. It feels, he said, “like a black market version of Amazon Web Services.” That official says the malware that runs the botnet assigns infected hosts different roles — for example, more powerful systems might be used as DNS servers, while infected systems behind home routers may be infected with a “reverse proxy,” which lets the attackers control the system remotely.
Separately, Cybereason issued a report last week saying attackers are increasingly turning to domain generation algorithms (DGAs) generate large numbers of random Internet addresses to like to command and control servers. Gameover Zeus, for example, generated 1,000 domains every day, or 365,000 in one year, says the report. Attempting to block all these domains is hard for firewalls, network-filtering products and other security tools.
DGAs “are a near perfect communication method,” says the company. “They’re easy to implement, difficult to block, almost impossible to predict in advance, and can be quickly modified if the previously used algorithm becomes known.”
Creators use a number of techniques, the company says: One generates domains by randomly selecting seven letters, suffixing them with either the .ru or the .com top-level domains and prefixing them with the word “five” followed by a number (for example, five14.aheegdg,com). Another generated domains by randomly choosing two English words from a hard-coded list in the malware and linking them together under the .net top-level domain (for example, theirjuly.net).
The Dridex banking malware that leverages macros in Microsoft Office to infect systems links English words and parts of words chosen in random from a small list, suffixed by the .mn (Mongolia) and .me (Montenegro) top-level domains. The words are often broken, shifted and padded with random characters, significantly increasing the number of possible combinations and making detection much harder (for example, ALLOWCLIENTAXPALAGENT.ME). The well-known Angler exploit kit also uses a DGA.
Cybereason says it has also found a new DGA in malwae that seems to generate a random DWORD (a 32-bit integer, with a maximum value of approximately 4 million) which is converted to a hexadecimal format and suffix the result with either the .com, .net or .info TLDs (for example, 78E05B8B.NET).
Law enforcement and government agencies have tried to take control over top level domains at the source by going after the registrars, the report notes, but sometimes that doesn’t work.
Instead of looking for each DGA variant separately. Cybereason says vendors and security pros should look for behaviors associated with DGAs. “Just detecting a DGA incriminates a process as malicious since no legitimate process will ever use such a technique,” says the company.
Meanwhile, patching and updating systems to prevent infection will go a long way.
