In part one of this two-part series, the OpenDNS Company Blog focuses on the common “bag of tricks” that criminals use to avoid detection online.
Infosec experts often apply the phrase “know your enemy” when discussing the techniques used by malicious actors online. While every organization has its own unique threat model, the average sophistication level of financially-motivated attacks has increased in recent years. One of the reasons for the increase is the increasing availability of proven tools, infrastructure and operational techniques for carrying out successful attacks against business networks and endpoints.
Math != Stealth
Before talking about how bad guys hide their activity online, a brief word about applied cryptography: it won’t be discussed in detail, here. Encryption is a complex topic that is best left up to professional cryptographers. It’s also only a small piece of the puzzle when it comes to identifying would-be online attackers, who can be identified through a variety of methods before, during and after an attack.
Obfuscation and Evasion
Many modern information security systems have their roots in signature-based detection and blocklisting technologies that have been around for decades (antivirus being the most common example). To avoid detection, hackers rely on the ability to change malware signatures quickly in order to reuse the same piece of malware against a wide variety of targets.
One of the primary methods of disguising malware signatures is through the use of crypters. As a previous post on the OpenDNS Security Labs blog outlines, crypters allow criminals to rapidly change malware files:
These tools typically cut up the input file into pieces, encrypt them, and place them into another executable which has been specially crafted to reassemble the payload and have it run. These outer shells are updated multiple times per day to evade detection by security software, and many even employ server-side polymorphism on the malware repository, which means each individual victim will receive a distinct copy of the malicious file. It’s not hard to see why naive signature-based detection techniques cannot keep up with this style of distribution.
Crypters have made it much easier for attackers to hide their malware from security solutions that rely on automated file signature matching. Essentially, the file signature is no longer based on the ability of a malware author to rewrite/recompile the code for each attack campaign, but on a third party specialist that sells crypter software, which can itself be reused. Since most financially-motivated crime tends to strives to compromise as many targets as possible (although there are exceptions), criminals have favored this method of disguising file signatures in recent years.
Network-level obfuscation can also be accomplished through a number of methods to make an attacker’s traffic patterns and connections look random or disguise them as network traffic. From the same blog OpenDNS Security Labs blog post:
Previous versions of Pushdo have used DNS smokescreens, URL path randomization, and DGA fall back techniques for obscuring command and control (C2) communication.
Domain generation algorithms (DGAs) are another common method of making it difficult to detect malicious network connections. As detailed elsewhere on this blog, DGAs can create hundreds or thousands of domains that a machine checks daily, which can be used as command-and-control nodes for botnets or other infected machines. Generally, a combination of randomness and volume is used to disguise which domains are really being utilized for malicious communications.
Both of these methods, however, do still leave a trail of clues that security researchers can follow. You can read about methods for defeating crypters and DGAs in the aforementioned Labs blog post and here.
Old Fashioned OPSEC
Do you want to pass a confidential message to a coworker that’s private and secure? First, walk over to them. Next, tell them your message, quietly. That’s it! No encryption or Tor Hidden Services required.
OPSEC (operational security, in military parlance) is generic shorthand for the techniques people use to keep their plans or activities secret. Most OPSEC techniques can be decidedly low tech. For instance, sneakernets are one of the simplest ways of hiding your online activity — just stay offline. Accordingly, most of today’s online criminals try to keep activities like selling/purchasing crypters, renting time on botnets away from prying eyes, instead relying on Dark Web forums to carry out those activities.
Other simple “operational hygiene” techniques are commonly used by bad guys to hid their activity, such as one-time use email addresses. For example, the use of overlapping email addresses for registering domains connected with the Angler exploit kit and Bedep botnet have led the research to link the these two pieces of malicious infrastructure.
One of biggest developments of the last decade has been the specialization and professionalization of cybercrime. Today’s financially-motivated online criminals have an array of services, providers, and infrastructure that they can utilize to carry out attacks. A criminal might purchase malware from an online forum, an exploit kit to deliver the malware, rent time on a botnet to deliver command-and-control instructions to compromised machines. Sometimes, these services will be bundled into a single turnkey solution, which allows criminals to easily scale their operations and go after more targets.
Based on the writing of security blogger Brian Krebs, it seems that one of the biggest OPSEC problems for today’s criminals comes from simply having to operate businesses that caters to (and compete with) other criminals. Krebs has written extensively about several incidents where criminals have hacked one another.
Also, separation of providers makes it harder to keep OPSEC intact, every other “dumb customer” of a bulletproof hosting provider provides more information that infosec teams can use to zero in on the source of an attack. Dark Web forums also face a conundrum: in order to attract enough criminals to be useful, they still must be “known” to a certain subset of the criminal population. This very quality makes it difficult for these forums to avoid attracting attention from security researchers.
Join the OpenDNS Blog again next week, when we speak with OpenDNS Security Labs researcher Anthony Kasza about how researchers are finding new ways to uncover malicious behavior online.