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This document contains recommendations on how large Internet Service Providers (ISPs) can manage the effects of large numbers of bot infected computers used by their subscribers via various remediation techniques. At the time that this document was published, computers infected by bots and the users of those computers comprise a substantial number of users for large ISPs. Those Internet users are exposed to risks such as loss of personal data, increased susceptibility to online fraud and/or phishing, and becoming an inadvertent participant in or component of an online crime, spam, and/or phishing network. Mitigating the effects of and remediating the installations of bots affecting large numbers of Internet users will make it more difficult for bot nets to operate and could reduce the level of online crime on the Internet in general and/or on a particular ISP's network.
1.
Requirements Language
2.
Key Terminology
3.
Introduction and Problem Statement
4.
Important Notice of Limitations
5.
Detection, Notification and Remediation
5.1.
Detection of Bots
5.2.
Notification to Internet Users
5.3.
Remediation of Bot Infected Machines
5.4.
Guided Remediation Process
6.
Security Considerations
7.
IANA Considerations
8.
Contributors
9.
Normative References
Appendix A.
Document Change Log
Appendix B.
Open Issues
§
Authors' Addresses
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).
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This section defines the key terms used in this document.
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A "bot" (derived from the word "robot") refers to a program that is surreptitiously installed on a system in order to enable that system to automatically (or semi-automatically) perform a task or set of tasks typically under the command and control of a remote administrator, or "bot master." Bots are also known as "zombies." It is important to note that there are 'good' bots. Such benign bots are often found in such environments such as gaming and Internet Relay Chat (IRC) [RFC1459] (Oikarinen, J. and D. Reed, “Internet Relay Chat Protocol,” May 1993.), where a continual, interactive presence can be a requirement for participating in the games, interacting with a computing resource, or other purposes. However, for the purposes of this document, all mention of bots should assume that the bots involved are malicious in nature. Such malicious bots shall generally be assumed to have been deployed without the permission or conscious understanding of a particular Internet user. Thus, without a user's knowledge, bots may transform the user's computing device into a platform from which malicious activities are conducted.
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These are defined as concerted networks of bots capable of acting on instructions generated remotely. The malicious activities are either focused on the information on the local machine or acting to provide services for remote machines. Bots are highly customizable so they can be programmed to do many things. The major malicious activities include: identity theft, spam, denial of service attacks, key-logging, fraudulent DNS, proxy services, hosting and click fraud. Infection vectors include un-patched operating systems, software vulnerabilities, weak/non-existent passwords, malicious websites, un-patched browsers, malware and social engineering techniques to gain access to the user's computer. The detection and destruction of bots is an ongoing issue and also a constant battle between anti-virus developers and bot developers. Initially botnets utilized IRC to communicate but were easy to shutdown if the command and control server was identified and deactivated. However, with the introduction of P2P, HTTP and other technologies including encryption, bots are considerably more difficult to identify. As a result increased reliance is being placed on behavioral analysis both locally and remotely to identify bots.
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A computer, as used in the context of this document, is intended to encompass the various personal computing devices used by Internet users. This may include devices ranging from so-called personal computers, including laptops, desktops, and netbooks, as well as mobile phones, smart phones, home gateway devices, and other end user computing devices which are connected or can connect to the public Internet and/or private IP networks.
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This is short for "malicious software." In this case, malicious bots are considered a subset of malware, which could also include viruses and other similar types of software. Internet users can sometimes cause their computer to be infected with malware, which may include a bot or cause a bot to install itself, via inadvertently accessing a specific website, downloading a specific file, or other activities.
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Computers used by Internet users, which in this case are customers of an Internet Service Provider (ISP), can be infected with malware which may contain and/or install one or more bots on a computer. This can present a major problem for an ISP for a number of reasons (not to mention, of course, the problems created for users). First, these bots can be used to send spam, in some cases very large volumes of spam. This spam can result in extra cost for the ISPs in terms of wasted network, server, and/or personnel resources, among many other potential costs or side effects. Such spam can also negatively affect the reputation of the ISP, their customers, and the email reputation of the IP address space used by the ISP (often referred to simply as "IP reputation").
In addition, these bots can act as platform for directing, participating in, or otherwise conducting attacks on critical Internet infrastructure. Bots are frequently used as part of concerted Distributed Denial of Service (DDoS) attacks for criminal, political, anarchistic, or other motivations. For example, bots have been used to attack Internet resources and infrastructure ranging from web sites, to email servers and DNS servers, as well as the critical Internet infrastructure of entire countries.
While any computing device, including computers used by Internet users to the servers operated by ISPs and other organizations can be infected with bots, the majority of bot infections affect the computers used by Internet users. ISPs have a unique potential role when it comes to detecting botnets because they provide IP connectivity for the "good" and "bad" traffic coming from user systems. Furthermore, ISPs may also be in a unique position to be able to communicate to Internet users which are their customers, when customers computers may have been determined to have been or possibly have been infected with one or more bots.
From an end user perspective, knowing that their computer has been infected with one or more bots of very important information. Once they know this, they can take steps to remove the bot, protect themselves in the future, and resolve any problems which may stem from the bot infection. Given that bots can not only drain their local computing and network resources, but also enable the theft of personal information (including personal financial information), it is important to help users identify when they may have been infected with a bot.
As a result, the intent of this document is to provide a guide to ISPs and other organizations for the remediation of these computers infected with bots, so as to reduce the size of bot nets and minimize the potential harm that bots can inflict upon Internet infrastructure generally, as well as on individual Internet users. Efforts by ISPs and other organizations could therefore, over time, reduce the pool of computers infected with bots on the Internet, which in turn could result in smaller bot nets with less capability for disruption.
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The techniques described in this document in no way guarantee the remediation of all bots. Bot removal is potentially a task requiring specialized knowledge, skills and tools, and may be beyond the ability of average users. Attempts at bot removal may frequently be unsuccessful, or only partially successful, and may leave a user's system in an unstable and unsatisfactory state or even still infected. Attempts at bot removal can also result in side effects ranging from a loss of data or other files, all the way through partial or complete loss of system usability.
In general, the only way a user can be sure they have removed some of today's increasingly sophisticated malware is by "nuking-and-paving" the system: reformatting the drive, reinstalling the operating system and applications (including all patches) from scratch, and then restoring user files from a clean backup.
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The potential mitigation of bots is accomplished through a process of detection, notification to Internet users, and remediation of that bot with a variety of tools.
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An ISP must first identify that an Internet user, in this case a user that is assumed to be their customer or otherwise connected to the ISP's network, is determined to be infected, or likely to have been infected with a bot. The ISP should attempt to detect the presence of bots using methods, processes, and tools which maintain the privacy of the personally identifiable information of their customers. The ISP also should not block legitimate traffic in the course of bot detection, and should instead employ detection methods, tools, and processes which seek to be non-disruptive, as well as transparent to both Internet users as well as the people who are deploying and/or operating bot nets.
Detection methods, tools, and processes may include things such as analysis of specific network and/or application traffic flows (such as traffic to an email server), analysis of aggregate network and/or application traffic data, data feeds received from other ISPs and organizations (such as lists of the ISP's IP addresses which have been reported to have sent spam), feedback from the ISP's customers or other Internet users, as well as a wide variety of other possibilities. It is likely that a combination of all of the multiple bot detection data points will prove to be the most effective approach, in order to corroborate information of varying dependability or consistency, as well as to avoid or minimize the possibility of false positive identification of computers. Detection should also, where possible and feasible, attempt to classify a bot in order to confirm that it is malicious in nature, estimate the variety and severity of threats it may pose (such as spam bot, key logging bot, file distribution bot, etc.), and to determine a potential methods for eventual remediation.
Detection is also time-sensitive. If complex analysis is required and multiple confirmations are needed to confirm a bot is indeed present, then it is possible that the bot will do its damage before it can be stopped. This may mean that an ISP may need to balance the desire or need to definitively classify and/or confirm a bot, which may take an extended period of time, with the ability to predict the strong likelihood of a bot in a very short period of time. This also means that Internet users may benefit from the deployment of client-based software protections or other software tools, which can enable rapid performance of heuristically-based detection bot activity, such as the detection of a bot as it starts to communicate a bot net and execute some type of command. Any bot detection systems should also be capable of learning and adapting, either via manual intervention or automatically, in order to cope with a rapidly evolving threat.
As noted above, detection methods, tools, and processes should ensure that privacy of customers' personally identifiable information is maintained. While bot detection methods, tools, and processes are similar to spam and virus defenses deployed by the ISP for the benefits of their customers (and may be directly related to those defenses), attempts to detect bots should take into account the need of an ISP to take care to ensure that such personally identifiable information is properly protected. Finally, depending upon the geographic region within which an ISP operates, certain methods relating to bot detection may need to be included in relevant terms of service documents or other documents which are available to the customers of a particular ISP.
There are several bot detection methods, tools, and processes that an ISP may choose to utilize, as noted in the list below. It is important to note that the technical solutions available are relatively immature, and are likely to change over time, and to evolve rapidly in the coming years. While these items are described in relation to ISPs, they may also be applicable to organizations operating other networks, such as campus networks and enterprise networks.
- a.
- Where legally permissible or otherwise an industry accepted practice in a particular market region, an ISP may in some manner "scan" their IP space in order to detect un-patched or otherwise vulnerable hosts. This may provide the ISP with the opportunity to easily identify Internet users who appear to already be or are at great risk of being infected with a bot. Such scanning should be an unobtrusive and non-disruptive to users and user computers as possible, using tools which such as NMAP (http://www.nmap.org), Nessus (http://www.nessus.org), etc.
- b.
- An ISP may also communicate and share selected data, via feedback loops or other mechanisms, with various third parties. Feedback loops are consistently formatted feeds of real-time (or nearly real-time) abuse reports offered by threat data clearinghouses, security alert organizations, ISPs, and other organizations. The data may include, but is not limited to, lists of the IP addresses computers which have or are likely to have a bot running, domain names or fully qualified domain names (FQDNs) known to host malware and/or be involved in the command and control of bot nets, IP addresses know to host malware and/or be involved in the command and control of bot nets, recently tested or discovered techniques or detecting or remediating bot infections, new threat vectors, and other relevant information.
- c.
- An ISP may use Netflow [RFC3954] (Claise, B., “Cisco Systems NetFlow Services Export Version 9,” October 2004.) or other similar passive network monitoring to identify bots. For example, an ISP may be able to identify compromised hosts by identifying traffic destined to IP addresses associated with the command and control of bot nets.
- d.
- An ISP may use DNS-based techniques to perform detection. For example, a given classified bot may be known to query a specific list of domain names at specific times or on specific dates (in the example of the so-called "Konficker" bot network), typically by matching DNS queries to a well known list of domains associated with malware. In many cases such lists are distributed by or shared using third parties, such as threat data clearinghouses.
- e.
- User complaints: Because botted hosts are frequently used to send spam, the ISP servicing those botted hosts will normally receive complaints about that spam. Those complaints may be sent to RFC2142-specified [RFC2142] (Crocker, D., “MAILBOX NAMES FOR COMMON SERVICES, ROLES AND FUNCTIONS,” May 1997.) role accounts, such as abuse@ or postmaster@ or to abuse or security addresses specified by the site as part of its WHOIS (or other) contact data.
- f.
- ISPs may also discover likely botted hosts located at other sites; when legally permissible or otherwise an industry accepted practice in a particular market region, it may be worthwhile for ISPs to share evidence relating to those compromised hosts with the relevant remote ISP, with security researchers, and with blocklist operators.
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Once an ISP has detected a bot, or the strong likelihood of a bot, steps should be undertaken to inform the Internet user that they may have a bot-related problem. Depending upon a range of factors, from the technical capabilities of the ISP, to the technical attributes of their network, financial considerations, available server resources, available organizational resources, the number of likely infected computers detected at any given time, and the severity of any possible threats, among many other things, an ISP will decide the most appropriate method or methods for providing notification to one or more of their customers or Internet users. Such notification methods may include one or more of the following, as well as other possible methods not described below. It is important to note that none of these methods are guaranteed to be successful, as each has its own set of limitations. In addition, in some cases, and ISP may determine that a combination of two or more methods is most appropriate. Finally, notification is also considered time sensitive; if the user does not receive or view the notification or a timely basis, then a particular bot could launch an attack, exploit the user, or cause other harm.
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This is probably the most common form of notification used by ISPs. One drawback of using email is that it is not guaranteed to be viewed within a reasonable time frame, if at all. The user may be using a different primary email address than that which they have provided to the ISP. In addition, some ISPs do not provide an email account at all, as part of a bundle of Internet services, and/or do not have a need for or manner in which to request or retain the primary email addresses of Internet users of their networks. Another possibility is that the user, their email client, and/or their email servers could determine or classify such a notification as spam, which could delete the message or otherwise file it in an email folder that the user may not check on a regular and/or timely basis. Finally if the user's email credentials are compromised, then a hacker and/or a bot could simply login to the user's email account and delete the email before it is read by the user.
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A telephone call may be an effective means of communication in particularly high-risk situations. However, telephone calls may not be feasible due to the cost of making a large number of times, as measured in either time, money, organizational resources, server resources, or some other means. In addition, there is no guarantee that the user will answer their phone. To the extent that the telephone number called by the ISP can be answered by the infected computing device, the bot on that computer may be able to disconnect, divert, or otherwise interfere with an incoming call. Users may also interpret such a telephone notification as a telemarketing call and as such not welcome it, or not accept the call at all. Finally, even if a representative of the ISP is able to connect with and speak with a user, that user is very likely to lack the necessary technical experience to understand or be able to effectively deal with the threat.
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This form of notification is probably the least popular means of communication, due to both preparation time, delivery time and cost.
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Placing a user in a so-called walled garden is another approach that ISPs may take to notify users. This is an effective technique because it could be able to block all communication between the bot and the command and control channel, which may impair the ability of a bot to disrupt or block attempts to notify the user.
While in many cases, the user is almost guaranteed to view the notification message and take any appropriate remediation actions, this approach poses can pose other challenges. For example, it is not always the case that a user is actively using a computer that uses a web browser or which has a web browser actively running on it. In one case, a user could be playing a game online, via the use of a dedicated, Internet-connected game console. In another case, the user may not be using a computer with a web browser when they are placed in the walled garden and may instead be in the course of a telephone conversation, or may be expecting to receive a call, using a Voice Over IP (VOIP) device of some type. As a result, the ISP may feel the need to maintain a potentially lengthy white list of domains which are not subject to the typical restrictions of a walled garden, which could well prove to be an onerous task, from an operational perspective.
The ISP has several options to determine when to let the user out of the walled garden. One approach may be to let the user determine when to exit. This option is suggested when the purpose of the walled garden is to notify users and provide information on remediation only, particularly since notification is not a guarantee of successful remediation. It could also be the case that, for whatever reason, the user makes the judgement that they cannot then take the time to remediate their computer and that other online activities which they would like to resume are more important.
Once the user acknowledges the notification, then the user decides to either remediate and then exit the walled garden, or exit the walled garden without addressing the issue. Another approach may be to enforce a stricter policy and require the user to clean the computer prior to permitting the user to exit the walled garden, though this may not be technically feasible depending upon the type of bot, obfuscation techniques employed by a bot, and/or a range of other factors. Thus, the ISP may also need to support tools to scan the infected computer and determine whether it is still infected or rely on user judgement that the bot has been disabled or removed. One challenge with this approach is that if the user has multiple computers sharing a single IP address, such as via a common home gateway device which performs Network Address Translation (NAT), then the ISP may need to determine from user feedback or other means that all affected computers have been remediated, which may or may not be technically feasible.
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Instant Message (IM): Instant messaging provides the ISP with a simple means to communicate with the user. There are several advantages of using IM which makes it an attractive option. First, if the ISP provides IM service and the user subscribes to it then the user can be notified easily. Second, IM based notification can be cost effective means to communicate with the use. This can be achieved by signing up for IM service with the various popular IM providers and programatically messaging, if permitted by the acceptable usage policy, the notifications. However, it IM based notification can also be done manually by the ISP's support staff. Ideally, the ISP should allow the user to register the IM identity and seek permission to be contacted via this mean. Third, if the IM service provider supports offline messaging the user can be notified regardless of their signed in status. Essentially a message can be sent and when the user signs in they would receive it. There are several drawbacks with this communications method. First, there is a high probability that subscriber may interpret the communication to be spam and as such ignore it. Second, not every user uses IM and/or the user may not provide their IM identity to the ISP so some alternative means have to be used. Third, there maybe a privacy concern when the communication between the ISP and the end user is not secure and over a third party network and/or IM service. As such the notification must be discreet and not provide any personally identifiable information.
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Short Message Service (SMS): SMS allows the ISP send a brief description of the problem to notify the user of the issue. ISP should allow users to register their mobile number for notifications and also allow users to opt out if they do not wish to be notified. The primary advantage of SMS is that users are used to receiving text messages and are likely to read them. Although users may not act on it immediately if they are not in front of their computer system. One disadvantage is that ISPs may have to follow up with an alternate means of communication if since a SMS message is restricted to 166 characters and not all of the necessary information maybe conveyed in one message. Another disadvantage is the cost associated with SMS. The ISP has to either build its own SMS gateway to interface with the various wireless providers or use a third party provider to notify users. It is recommended that the ISP absorb the cost of notification and should always state in the notification that the message is free of charge to the user. Another small disadvantage is that it is possible to notify the wrong user if the intended user changes their mobile number but forgets to update it with the ISP.
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Near real-time notification to the user's web browser is another technique that may be utilized for notifying the user, though how such a system might operate is outside the scope of this document. Such a notification could have a comparative advantage over a walled garden notification, in that it does not restrict traffic to a specified list of destinations in the same way that a walled garden by definition would. However, as with a walled garden notification, there is no guarantee that a user is at any given time making use of a web browser, though such a system could certainly provide a notification when such a browser is eventually used. Compared to a walled garden, a web browser notification is probably preferred from the perspective of Internet users, as it does not have the risk of disrupting non-web sessions, such as online games, etc. (as noted in Section 5.2.4 (Walled Garden Notification)).
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This section covers the different options available to remediate a computer, which means to remove, disable, or otherwise render a bot harmless. Prior to this step, an ISP has detected the bot, notified the user that one of their computers is infected with a bot, and now has to provide some means to clean the PC. The generally recommended approach is to provide the necessary tools and education to the user so that they may perform bot remediation themselves.
For example, this may include the creation of a special Security Web Portal. This should be a well-publicized security portal to which a user with a bot problem can be directed to for remediation. This Security Web Portal should clearly explain why the user was notified and may include an explanation of what bots are and the threats that they pose. There should be a clear explanation of the steps that the user should take in order to clean the computers and provide information on how users can keep the computer free of future infections. The Security Web Portal should have a guided process that takes non technical users through the remediation process.
In terms of the text user to explain what bots are and the threat they pose, something simple such as this may suffice:
"What is a bot? A bot is a piece of software, generally installed on your machine without your knowledge, which either sends spam or tries to steal your personal information. They can be very difficult to spot, though you may have noticed that your computer is running much more slowly than usual or you notice regular disk activity even when you are not doing anything. Ignoring this problem is not really an option since your personal information is currently at risk. Thus, bots need to be removed to protect your data and your personal information."
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Minimally the Guided Remediation Process should include options and/or recommendations on how a user should:
There are many cases where a user may not be a residential user, in which case some of these steps may not apply. For example, the user may be part of a business, educational institution, non-profit company, or other organization. In these cases, the user should immediately seek out the support of their information technology support team.
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Scanning systems for missing patches, while a good and necessary task, may nonetheless result in systems being knocked offline.
Conveying a system to a third party for cleaning may result in sensitive contents of that system (confidential email or images, unauthorized access to remote systems via stored passwords, etc.) being inadvertently disclosed to the third party.
Passive network monitoring, even of encrypted traffic, may result in sensitive information leaking (e.g., merely knowing that a user is connecting to a site about a particular subject may prompt one to infer an interest in that particular subject).
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There are no IANA considerations in this document.
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The authors wish to acknowledge the following individuals for their textual contribution to and detailed reviews of this document:
Joe St. Sauver, University of Oregon and Internet2 (joe@uoregon.edu)
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| [RFC1459] | Oikarinen, J. and D. Reed, “Internet Relay Chat Protocol,” RFC 1459, May 1993 (TXT). |
| [RFC2119] | Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). |
| [RFC2142] | Crocker, D., “MAILBOX NAMES FOR COMMON SERVICES, ROLES AND FUNCTIONS,” RFC 2142, May 1997 (TXT, HTML, XML). |
| [RFC3954] | Claise, B., “Cisco Systems NetFlow Services Export Version 9,” RFC 3954, October 2004 (TXT). |
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[RFC Editor: This section is to be removed before publication]
-00 version:
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[RFC Editor: This section is to be removed before publication]
Could use some informational references in Section 3
Fix the odd list spacing in Section 5.1
Add some point about notification to large networks may not be useful -- such as coffee shops or hotels with WiFi networks.
Consider combining 5.b and 5.f., and possibly re-wording some of the other items.
Consider adding mention to the use of ccleaner in section 5.4
Significantly revise and expand section 5.4
Add discussion of root kits and other bits of malware that may actively resist detection and removal (e.g., attempting to disinfect a system while running an infected OS can be a rather futile exercise; you have a much better chance of detecting malware if you mount the infected disk on a third party system for review and disinfection)
add discussion on restoring files from the backups if nuke and pave is required.
add discussion of user education to help prevent repeat infections
consider adding discussion of the ISP's role in the remediation process -- I think this is a key consideration. Liability issues, cost issues and other factors should be laid out so that users understand why the ISP doesn't just "do it for them."
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| Jason Livingood | |
| Comcast Cable Communications | |
| One Comcast Center | |
| 1701 John F. Kennedy Boulevard | |
| Philadelphia, PA 19103 | |
| US | |
| Email: | jason_livingood@cable.comcast.com |
| URI: | http://www.comcast.com |
| Nirmal Mody | |
| Comcast Cable Communications | |
| One Comcast Center | |
| 1701 John F. Kennedy Boulevard | |
| Philadelphia, PA 19103 | |
| US | |
| Email: | nirmal_mody@cable.comcast.com |
| URI: | http://www.comcast.com |
| Mike O'Reirdan | |
| Comcast Cable Communications | |
| One Comcast Center | |
| 1701 John F. Kennedy Boulevard | |
| Philadelphia, PA 19103 | |
| US | |
| Email: | michael_oreirdan@cable.comcast.com |
| URI: | http://www.comcast.com |