Command and control (malware)

For other uses of the term, see Command and control (disambiguation)

In the field of computer security, command and control (C&C) infrastructure consists of servers and other technical infrastructure used to control malware in general, and, in particular, botnets. Command and control servers may be either directly controlled by the malware operators, or themselves run on hardware compromised by malware. Fast-flux DNS can be used as a way to make it difficult to track down the control servers, which may change from day to day. Control servers may also hop from DNS domain to DNS domain, with domain generation algorithms being used to create new DNS names for controller servers.

In some cases, computer security experts have succeeded in destroying or subverting malware command and control networks, by, among other means, seizing servers or getting them cut off from the Internet, denying access to domains that were due to be used by malware to contact its C&C infrastructure, and, in some cases, breaking into the C&C network itself. In response to this, C&C operators have resorted to using techniques such as overlaying their C&C networks on other existing benign infrastructure such as IRC or Tor, using peer-to-peer networking systems that are not dependent on any fixed servers, and using public key encryption to defeat attempts to break into or spoof the network.

Architecture of Command and Control types

The methods on which a Command and control is built for communications. The architecture evolved over time, and not all C&C exhibit the same topology for command and control. Advanced topology is more resilient to shutdown, enumeration or discovery. However, some topologies limit the marketability of the botnet to third parties. Typical botnet topologies are star, multi-server, hierarchical and random.

Client–server model

A network based on the client-server model, where individual clients request services and resources from centralized servers

The Client–server model appeared on the first types of botnets that appeared online and has usually been built on Internet Relay Chat or by using Domains or Websites which will have the commands listed for the botnet to be controlled. In IRC commands tend to be simpler and botnets tend to be smaller if built on an IRC network. Since IRC networks require lowbandwith and use simple methods for communication they have been also used to host botnets and are tend to simple in construction and have been used many times for coordinating DDoS attacks or spam campaigns while switching channels to avoid being taken down. Although blocking certain keywords has sometimes proved effective in stopping a botnet based on IRC.

Most of the largest botnets that have been built tended to use domains rather than IRC in their construction.(see Rustock botnet see also Srizbi botnet.) Almost always they have been hosted with bullet proof hosting services.(See Bulletproof hosting.) Since most of the time botnets based on the Client-server model have been taken down in a matter of time, hackers have moved toward P2P as an alternative to avoid botnet takedowns.

Botnet servers are typically redundant, linked for greater redundancy so as to reduce the threat of a takedown. Actual botnet communities usually consist of one or several controllers that rarely have highly developed command hierarchies; they rely on individual peer-to-peer relationships.

The botnet server structure mentioned above has inherent vulnerabilities and problems. For example, finding one server with one botnet channel can often reveal the other servers, as well as their bots. A botnet server structure that lacks redundancy is vulnerable to at least the temporary disconnection of that server. However, recent IRC server software includes features to mask other connected servers and bots, eliminating that approach.

Peer-to-peer

A peer-to-peer (P2P) network in which interconnected nodes ("peers") share resources amongst each other without the use of a centralized administrative system

Since most of the time IRC networks and Domains can be taken down with time, hackers have moved on to P2P as a way to make it harder to be taken down. Some have even been known to use encryption as a way to secure or lock down the botnet from others, most of the time when they use encryption it is Public-Key encryption and has presented challenges in both implementing it and breaking it.(See Gameover ZeuS See also ZeroAccess botnet.)

Some newer botnets are almost entirely P2P. Command and control is embedded into the botnet rather than relying on external servers, thus avoiding any single point of failure and evading many countermeasures. Commanders can be identified just through secure keys, and all data except the binary itself can be encrypted. For example, a spyware program may encrypt all suspected passwords with a public key that is hard-coded into it, or distributed with the bot software. Only with the private key (known only by the botnet operators) can the data captured by the bot be read.

In the P2P method of command and control the bot only tends to know a list of peers of which it can send commands to and that are passed on to other peers further down the botnet. The list tends to be around 256 peers which allows it to be small enough for it to allow commands to be quickly passed on to other peers and makes it harder to disrupt the operation of the botnet while allowing it to remain online if major numbers of peers are taken down in a takedown effort.

Systems Used for Command and Control

There have been different ways Command and Control (C&C) have been implemented. Here are some of the common and well known types of C&C listed.

Domains as C&C

This is one of the earliest types of C&C known. A zombie computer access a certain webpage or domain(s) in which commands are listed for it to be controlled. The advantages of using a webpages or domains as C&C are most of the time simpler coding and easy to update and maintain a large botnet without much issues. The disadvantages of using webpages or domains is high bandwidth needed if a large botnet is built, also many domains have been seized by government agencies in order to take down a botnets without much trouble or effort. The domains can be also a target for Denial-of-service attacks which may take a domain based botnet offline.

IRC as C&C

Since IRC networks require low bandwidth and use simple methods for communication they have been also used to host botnets and are tend to simple in construction and have been used many times for coordinating DDoS attacks or spam campaigns while switching channels to avoid being taken down. Although blocking certain keywords has sometimes proved effective in stopping a botnet based on IRC.

P2P as C&C

Peer to Peer botnets with Command and Control based on Peer to Peer technology have been more less recent in the threat landscape. Since most of the time IRC networks and Domains can be taken down with time, hackers have moved on to P2P as a way to make it harder to be taken down. Some have even been known to use encryption as a way to secure or lock down the botnet from others, most of the time when they use encryption it is Public-Key encryption and has presented challenges in both implementing it and breaking it.

See also

• Malware
• Advanced Persistent Threat
• Zombie (computer science)
• Botnet
• Low Orbit Ion Cannon
• ZeroAccess botnet
• Zeus (malware)

External Links

• LOIC IRC-0 - An Open-Source IRC Botnet for Network Stress Testing
• LOIC SLOW IRC Now Able to Use Webpages And IRC as C&C
• Build your own botnet with open source software