Websense researchers Stephan Chenette and Armin Buescher took a random sampling of nearly 200,000 malicious programs and categorized them by behavior, including how the malware communicated over the network. Malware typically reaches out over the network to request commands from a command-and-control (C&C) server or to exfiltrate intellectual property or other sensitive corporate information, they said during a presentation at last week's SOURCE Boston security conference.
"If the point isn't the complete destruction of data, what's going to happen is that the attackers are going to install malware in the network and the malware will eventually communicate out," Chenette said.
In the end, they found that 46 percent of malware communicates out in the first 60 seconds. The result hews closely to a 2009 paper presented at the USENIX Workshop on Large-Scale Exploits and Emergent Threats (LEET), which found that 46 percent of malware caught in the Anubis malware-analysis platform communicated using TCP and another 27 percent used UDP. In that study, a total of 55 percent of traffic communicated using some identifiable network protocol.
Another reason to look for communications? Malware is constantly changing its signature using encryption and packing, but the way an attacker chooses to communicate with his programs changes far less frequently. The researchers found that more than a quarter of malware identified by network behavior was not detected by any antivirus scanner.
[Russian botnets mostly use crypto, Chinese attacks mostly don't, but attack analysis finds that the bad guys are increasingly using better encryption. See Malware Encryption Efforts Mixed, But Getting Stronger.]
Companies that seek out any malware communications that appear in their networks are more like to catch the attacks, agrees Jose Nazario, senior manager for the security research team at Arbor Networks. Arbor clients have frequently detected malware using communications that were not detected using up-to-date antivirus, he says. While binaries change frequently, the protocols that malware uses to communicate, as well as the servers with which they communicate, change less often.
"These sorts of protocols that these guys design for allowing the bots to communicate back to the mothership are relatively static," Nazario says. "I would argue that it is relatively expensive for hackers to alter their protocols because you always risk losing bots, leaving a significant chunk of the botnet behind, when you upgrade the protocol and move them over."
Joe Stewart, director of malware research for Dell SecureWorks, agrees that malware and botnet communications are relatively static.
"We sometimes see signatures that we have written for malware [communications] that work for years," he says.
And companies that do monitor for malware communications stand to catch more than half of the programs. It's likely that the Websense findings -- 46 percent, or 55 percent in the case of the Anubis study -- may be a low estimate. Typically, researchers cranking through a large volume of malware only listen during the first minute to be as efficient as possible. Patient attackers are already wise to the tactic and will delay communications outside that time, perhaps evading detection, Stewart says. And other malware may use nonstandard ways of communicating that are more covert.
"There is malware that doesn't have to communicate to work," Stewart says. "Maybe it is only going to alter how something on your system works. Maybe it will change your host file and cause your DNS queries to answer something other than the name you wanted when you are, for example, looking up Yahoo."
DNS Changer did exactly that. The program changed the listing of the domain name servers used by the compromised systems to reroute a victim's Internet queries.
The good news is that companies looking for malware communications would have caught signs of DNS Changer, as well, if they were armed with the Internet addresses of the fake DNS servers used by the malware.
While looking at all network traffic can be daunting, there are ways to whittle down the amount of packets that need inspection, says Stewart. Looking for anomalies in specific protocols, especially HTTP, can help companies slim down their list of suspects.
"Look into that and see what traffic, what requests you are seeing that look completely different from the other requests," he says. "That will also have a lot of stuff that it not malicious at all, but it is a much smaller subset of things to go through ... if you know what to look for."
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