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Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force J. Livingood 3 Internet-Draft N. Mody 4 Intended status: Informational M. O'Reirdan 5 Expires: August 14, 2010 Comcast 6 February 10, 2010 8 Recommendations for the Remediation of Bots in ISP Networks 9 draft-oreirdan-mody-bot-remediation-05 11 Abstract 13 This document contains recommendations on how Internet Service 14 Providers can manage the effects of computers used by their 15 subscribers, which have been infected with malicious bots, via 16 various remediation techniques. Internet users with infected 17 computers are exposed to risks such as loss of personal data, as well 18 as increased susceptibility to online fraud and/or phishing. Such 19 computers can also become an inadvertent participant in or component 20 of an online crime network, spam network, and/or phishing network, as 21 well as be used as a part of a distributed denial of service attack. 22 Mitigating the effects of and remediating the installations of 23 malicious bots will make it more difficult for botnets to operate and 24 could reduce the level of online crime on the Internet in general 25 and/or on a particular Internet Service Provider's network. 27 Status of this Memo 29 This Internet-Draft is submitted to IETF in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF), its areas, and its working groups. Note that 34 other groups may also distribute working documents as Internet- 35 Drafts. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 The list of current Internet-Drafts can be accessed at 43 http://www.ietf.org/ietf/1id-abstracts.txt. 45 The list of Internet-Draft Shadow Directories can be accessed at 46 http://www.ietf.org/shadow.html. 48 This Internet-Draft will expire on August 14, 2010. 50 Copyright Notice 52 Copyright (c) 2010 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the BSD License. 65 This document may contain material from IETF Documents or IETF 66 Contributions published or made publicly available before November 67 10, 2008. The person(s) controlling the copyright in some of this 68 material may not have granted the IETF Trust the right to allow 69 modifications of such material outside the IETF Standards Process. 70 Without obtaining an adequate license from the person(s) controlling 71 the copyright in such materials, this document may not be modified 72 outside the IETF Standards Process, and derivative works of it may 73 not be created outside the IETF Standards Process, except to format 74 it for publication as an RFC or to translate it into languages other 75 than English. 77 Table of Contents 79 1. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 80 2. Key Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 81 3. Introduction and Problem Statement . . . . . . . . . . . . . . 6 82 4. Important Notice of Limitations and Scope . . . . . . . . . . 7 83 5. Detection of Bots . . . . . . . . . . . . . . . . . . . . . . 8 84 6. Notification to Internet Users . . . . . . . . . . . . . . . . 12 85 7. Remediation of Compters Infected with a Bot . . . . . . . . . 17 86 8. Guided Remediation Process . . . . . . . . . . . . . . . . . . 18 87 9. Professionally-Assisted Remediation Process . . . . . . . . . 20 88 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 89 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 90 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21 91 13. Informative references . . . . . . . . . . . . . . . . . . . . 21 92 Appendix A. Document Change Log . . . . . . . . . . . . . . . . . 22 93 Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . . 23 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 96 1. Requirements Language 98 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 99 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 100 document are to be interpreted as described in [RFC2119]. 102 2. Key Terminology 104 This section defines the key terms used in this document. 106 2.1. Malicious Bots, or Bots 108 A malicious "bot" (derived from the word "robot", hereafter simply 109 referred to as a "bot") refers to a program that is surreptitiously 110 installed on a system in order to enable that system to automatically 111 (or semi-automatically) perform a task or set of tasks typically 112 under the command and control of a remote administrator, or "bot 113 master." Bots are also known as "zombies". 115 It is important to note that there are 'good', or benign bots. Such 116 benign bots are often found in such environments such as gaming and 117 Internet Relay Chat (IRC) [RFC1459], where a continual, interactive 118 presence can be a requirement for participating in the games, 119 interacting with a computing resource, or other purposes. Since such 120 benign bots are performing useful, lawful, and non-disruptive 121 functions, there is no reason for a provider to monitor for their 122 presence and/or alert users to their presence. 124 Thus, while there may be benign bots, for the purposes of this 125 document all mention of bots shall assume that the bots involved are 126 malicious in nature. Such malicious bots shall generally be assumed 127 to have been deployed without the permission or conscious 128 understanding of a particular Internet user. Thus, without a user's 129 knowledge, bots may transform the user's computing device into a 130 platform from which malicious activities can be conducted. In 131 general, installation of a malicious bot without user knowledge and 132 consent is considered in most regions to be unlawful, and the 133 activities of malicious bots typically involve unlawful or other 134 maliciously disruptive activities. 136 2.2. Bot Networks, or Botnets 138 These are defined as concerted networks of bots capable of acting on 139 instructions generated remotely. The malicious activities are either 140 focused on the information on the local machine or acting to provide 141 services for remote machines. Bots are highly customizable so they 142 can be programmed to do many things. The major malicious activities 143 include: identity theft, spam, distributed denial of service (DDoS) 144 attacks, key-logging, fraudulent DNS (pharming), proxy services, fast 145 flux hosting and click fraud. 147 Infection vectors include un-patched operating systems, software 148 vulnerabilities, weak/non-existent passwords, malicious websites, un- 149 patched browsers, malware, vulnerable helper applications and social 150 engineering techniques to gain access to the user's computer. The 151 detection and destruction of bots is an ongoing issue and also a 152 constant battle between the internet security community, network 153 security engineers and bot developers. 155 Initially, bots used IRC to communicate but were easy to shutdown if 156 the command and control server was identified and deactivated. Newer 157 command and control methods have evolved, such that those currently 158 employed by bot masters make them much more resistant to 159 deactivation. With the introduction of P2P, HTTP and other resilient 160 communication protocols along with the widespread adoption of 161 encryption, bots are considerably more difficult to identify and 162 isolate from typical network usage. As a result increased reliance 163 is being placed on anonmaly detection and behavioral analysis, both 164 locally and remotely, to identify bots. 166 2.3. Computer 168 A computer, as used in the context of this document, is intended to 169 refer to a computing device that connects to the Internet. This 170 encompasses devices used by Internet users such as personal 171 computers, including laptops, desktops, and netbooks, as well as 172 mobile phones, smart phones, home gateway devices, and other end user 173 computing devices which are connected or can connect to the public 174 Internet and/or private IP networks. 176 Increasingly, other household systems and devices contain embedded 177 computers which are connected to or can connect to the public 178 Internet and/or private IP networks. However, these devices may not 179 be under interactive control of the Internet user, such as may be the 180 case with various smart home and smart grid devices. 182 2.4. Malware 184 This is short for malicious software. In this case, malicious bots 185 are considered a subset of malware. Other forms of malware could 186 include viruses and other similar types of software. Internet users 187 can sometimes cause their computer to be infected with malware, which 188 may include a bot or cause a bot to install itself, via inadvertently 189 accessing a specific website, downloading a specific file, or other 190 activities. 192 Alternatively, Internet-connected computers may become infected with 193 malware through externally initiated malicious activities such as the 194 exploitation of vulnerabilities or the brute force guessing of access 195 credentials. 197 2.5. Fast Flux 199 DNS Fast Fluxing occurs when a domain is bound in DNS using A records 200 to multiple IP addresses, each of which has a very short Time To Live 201 (TTL) value associated with it. This means that the domain resolves 202 to varying IP addresses over a short period of time. 204 DNS Fast Flux is typically used in conjunction with proxies which 205 then route the web requests to the real host which serves the data 206 being sought. The proxies are normally hosted on compromised user 207 computers. The effect of this is to make the detection of the real 208 host for a piece of content much more difficult and to ensure that 209 the site remains up for as long as possible. 211 3. Introduction and Problem Statement 213 Computers used by Internet users, which in this case are customers of 214 an Internet Service Provider (ISP), can be infected with malware 215 which may contain and/or install one or more bots on a computer. 216 This can present a major problem for an ISP for a number of reasons 217 (not to mention of course the problems created for users). First, 218 these bots can be used to send spam, in some cases very large volumes 219 of spam [Spamalytics: An Empirical Analysis of Spam Marketing 220 Conversion]. This spam can result in extra cost for the ISPs in 221 terms of wasted network, server, and/or personnel resources, among 222 many other potential costs and side effects. Such spam can also 223 negatively affect the reputation of the ISP, their customers, and the 224 email reputation of the IP address space used by the ISP (often 225 referred to simply as 'IP reputation'). 227 In addition, these bots can act as platforms for directing, 228 participating in, or otherwise conducting attacks on critical 229 Internet infrastructure [Emerging Cyber Threats Report for 2009: 230 Data, Mobility and Questions of Responsibility will Drive Cyber 231 Threats in 2009 and Beyond]. Bots are frequently used as part of 232 concerted Distributed Denial of Service (DDoS) attacks for criminal, 233 political or other motivations [The Gh0st in the Shell: Network 234 Security in the Himalayas] [The snooping dragon: social-malware 235 surveillance of the Tibetan movement]. For example, bots have been 236 used to attack Internet resources and infrastructure ranging from web 237 sites, to email servers and DNS servers, as well as the critical 238 Internet infrastructure of entire countries [Battling Botnets and 239 Online Mobs: Estonia's Defense Efforts during the Internet War] 240 [Cyberspace as a Combat Zone: The Phenomenon of Electronic Jihad]. 241 Motivations for such coordinated DDoS attacks can range from criminal 242 extortion attempts through to online protesting and nationalistic 243 fervor [Case Study: How a Bookmaker and a Whiz Kid Took On a 244 DDOS-based Online Extortion Attack]. 246 While any computing device can be infected with bots, the majority of 247 bot infections affect the personal computers used by Internet end 248 users. As a result of the role of ISPs in providing IP connectivity, 249 among many other services, to Internet users, these ISPs are in a 250 unique position to be able to attempt to detect and observe bot nets 251 operating in their networks. Furthermore, ISPs may also be in a 252 unique position to be able to communicate to Internet users which are 253 their customers, when customers' computers may have been determined 254 to have been or possibly have been infected with one or more bots. 256 From an end user perspective, knowing that their computer has been 257 infected with one or more bots is very important information. Once 258 they know this, they can take steps to remove the bot, protect 259 themselves in the future, and resolve any problems which may stem 260 from the bot infection. Given that bots can drain local computing 261 and network resources, enable theft of personal information 262 (including personal financial information), enable the computer to be 263 used from criminal activities (that may result in the Internet user 264 being legally culpable), destroy or leave the PC in an unrecoverable 265 state via 'kill switch' bot technologies, it is important to notify 266 the user that they may be infected with a bot. 268 As a result, the intent of this document is to provide a guide to 269 ISPs and other organizations for the remediation of these computers 270 infected with bots, so as to reduce the size of bot nets and minimize 271 the potential harm that bots can inflict upon Internet infrastructure 272 generally, as well as on individual Internet users. Efforts by ISPs 273 and other organizations could therefore, over time, reduce the pool 274 of computers infected with bots on the Internet, which in turn could 275 result in smaller bot nets with less capability for disruption. 277 The potential mitigation of bots is accomplished through a process of 278 detection, notification to Internet users, and remediation of that 279 bot with a variety of tools, as described later in this document. 281 4. Important Notice of Limitations and Scope 283 The techniques described in this document in no way guarantee the 284 remediation of all bots. Bot removal is potentially a task requiring 285 specialized knowledge, skills and tools, and may be beyond the 286 ability of average users. Attempts at bot removal may frequently be 287 unsuccessful, or only partially successful, and may leave a user's 288 system in an unstable and unsatisfactory state or even in a state 289 where it is still infected. Attempts at bot removal can also result 290 in side effects ranging from a loss of data or other files, all the 291 way through partial or complete loss of system usability. 293 In general, the only way a user can be sure they have removed some of 294 today's increasingly sophisticated malware is by 'nuking-and-paving' 295 the system: reformatting the drive, reinstalling the operating system 296 and applications (including all patches) from scratch, and then 297 restoring user files from a clean backup. However the introduction 298 of BIOS-based malware may mean that, in some cases, this will not be 299 enough and may prove to be more than any end user can be reasonably 300 expected to resolve. Experienced users would have to reflash BIOS in 301 their machines in order to remove BIOS-based malware. 303 Devices with embedded operating systems, such as video gaming 304 consoles and smart home appliances, will most likely be beyond a 305 user's capability to remediate by themselves, and will typically 306 require the aid of vendor-specific advice, updates and tools. Care 307 must be taken when imparting remediation advice to Internet users 308 given the increasingly wide array of computing devices that can be, 309 or could be, infected by bots in the future. 311 5. Detection of Bots 313 An ISP must first identify that an Internet user, in this case a user 314 that is assumed to be their customer or otherwise connected to the 315 ISP's network, is determined to be infected, or likely to have been 316 infected with a bot. The ISP must attempt to detect the presence of 317 bots using methods, processes, and tools which maintain the privacy 318 of the personally identifiable information (PII) of their customers. 319 The ISP also must not block legitimate traffic in the course of bot 320 detection, and must instead employ detection methods, tools, and 321 processes which seek to be non-disruptive, as well as being 322 transparent to Internet users and end-user applications. 324 Detection methods, tools, and processes may include things such as 325 analysis of specific network and/or application traffic flows (such 326 as traffic to an email server), analysis of aggregate network and/or 327 application traffic data, data feeds received from other ISPs and 328 organizations (such as lists of the ISP's IP addresses which have 329 been reported to have sent spam), feedback from the ISP's customers 330 or other Internet users, as well as a wide variety of other 331 possibilities. It is likely that a combination of multiple bot 332 detection data points will prove to be an effective approach in order 333 to corroborate information of varying dependability or consistency, 334 as well as to avoid or minimize the possibility of false positive 335 identification of computers. Detection should also, where possible 336 and feasible, attempt to classify a bot in order to confirm that it 337 is malicious in nature, estimate the variety and severity of threats 338 it may pose (such as spam bot, key-logging bot, file distribution 339 bot, etc.), and to determine potential methods for eventual 340 remediation. However, given the dynamic nature of botnet management 341 and the criminal incentives to seek quick financial rewards, botnets 342 frequently update or change their core malicious capabilities. As a 343 consequence, botnets that are initially detected and classified by 344 the ISP as one particular type of bot need to be continuously 345 monitored and tracked in order to correctly identify the threat they 346 pose at any particular point in time. 348 Detection is also time-sensitive. If complex analysis is required 349 and multiple confirmations are needed to confirm a bot is indeed 350 present, then it is possible that the bot may cause some damage (to 351 either the infected computer or a remotely targeted system) before it 352 can be stopped. This may mean that an ISP may need to balance the 353 desire or need to definitively classify and/or confirm a bot, which 354 may take an extended period of time, with the ability to predict the 355 strong likelihood of a bot in a very short period of time. This 356 'definitive-vs-likely' challenge is difficult and, when in doubt, 357 ISPs should probably err on the side of caution by communicating when 358 a likely bot infection has taken place. This also means that 359 Internet users may benefit from the deployment of client-based 360 software protections or other software tools, which can enable rapid 361 performance of heuristically-based detection bot activity, such as 362 the detection of a bot as it starts to communicate a bot net and 363 execute some type of command. Any bot detection systems should also 364 be capable of learning and adapting, either via manual intervention 365 or automatically, in order to cope with a rapidly evolving threat. 367 As noted above, detection methods, tools, and processes should ensure 368 that privacy of customers' PII is maintained. While bot detection 369 methods, tools, and processes are similar to spam and virus defenses 370 deployed by the ISP for the benefit of their customers (and may be 371 directly related to those defenses), attempts to detect bots should 372 take into account the need of an ISP to take care to ensure any PII 373 collected or incidentally detected is properly protected. The 374 definition of PII varies from one jurisdiction to the next so proper 375 care must be taken to ensure that any actions taken comply with 376 legislation and good practice in the jurisdiction in which the PII is 377 gathered. Finally, depending upon the geographic region within which 378 an ISP operates, certain methods relating to bot detection may need 379 to be included in relevant terms of service documents or other 380 documents which are available to the customers of a particular ISP. 382 There are several bot detection methods, tools, and processes that an 383 ISP may choose to utilize, as noted in the list below. It is 384 important to note that the technical solutions available are 385 relatively immature, and are likely to change over time, evolving 386 rapidly in the coming years. While these items are described in 387 relation to ISPs, they may also be applicable to organizations 388 operating other networks, such as campus networks and enterprise 389 networks. 391 a. Where legally permissible or otherwise an industry accepted 392 practice in a particular market region, an ISP may in some manner 393 "scan" their IP space in order to detect un-patched or otherwise 394 vulnerable hosts. This may provide the ISP with the opportunity 395 to easily identify Internet users who appear to already be or are 396 at great risk of being infected with a bot. ISP's should note 397 that some types of port scanning may leave network services in a 398 hung state or render them unusable due to common frailties, and 399 that many modern firewall and host-based intrusion detection 400 implementations may alert the Internet user to the scan. As a 401 result the scan may be interpreted as a malicious attack against 402 the computer. Vulnerability scanning has a higher probability of 403 leaving accessible network services and applications in a damaged 404 state and will often result in a higher probability of detection 405 by the Internet user and subsequent interpretation as a targeted 406 attack. Depending upon the vulnerability being scanned, some 407 automated methods of vulnerability checking may result in data 408 being altered or created afresh on the Internet users computer 409 which be a problem in many legal environments. 411 b. An ISP may also communicate and share selected data, via feedback 412 loops or other mechanisms, with various third parties. Feedback 413 loops are consistently formatted feeds of real-time (or nearly 414 real-time) abuse reports offered by threat data clearinghouses, 415 security alert organizations, other ISPs, and other 416 organizations. The data may include, but is not limited to, 417 lists of the IP addresses computers which have or are likely to 418 have a bot running, domain names or fully qualified domain names 419 (FQDNs) known to host malware and/or be involved in the command 420 and control of botnets, IP addresses know to host malware and/or 421 be involved in the command and control of botnets, recently 422 tested or discovered techniques or detecting or remediating bot 423 infections, new threat vectors, and other relevant information. 424 Good examples of this include SNDS from Microsoft, XBL and PBL 425 from Spamhaus and the DSHIELD AS tool from the SANS Institue. 427 c. An ISP may use Netflow [RFC3954] or other similar passive network 428 monitoring to identify network anomalies that may be indicative 429 of botnet attacks or bot communications. For example, an ISP may 430 be able to identify compromised hosts by identifying traffic 431 destined to IP addresses associated with the command and control 432 of botnets. In addition, bots can be idenfied when a remote host 433 is under a DDoS attack because computers participating in the 434 attack will likely be infected by a bot, frequently as observed 435 at network borders. 437 d. An ISP may use DNS-based techniques to perform detection. For 438 example, a given classified bot may be known to query a specific 439 list of domain names at specific times or on specific dates (in 440 the example of the so-called "Conficker" bot), often by matching 441 DNS queries to a well known list of domains associated with 442 malware. In many cases such lists are distributed by or shared 443 using third parties, such as threat data clearinghouses. 445 e. User complaints: Because hosts infected by bots are frequently 446 used to send spam or participate in DDoS attacks, the ISP 447 servicing those hosts will normally receive complaints about the 448 malicious network traffic. Those complaints may be sent to 449 RFC2142-specified [RFC2142] role accounts, such as abuse@ or 450 postmaster@ or to abuse or security addresses specified by the 451 site as part of its WHOIS (or other) contact data. 453 f. ISPs may also discover likely bot infected hosts located at other 454 sites; when legally permissible or otherwise an industry accepted 455 practice in a particular market region, it may be worthwhile for 456 ISPs to share evidence relating to those compromised hosts with 457 the relevant remote ISP, with security researchers, and with 458 blocklist operators. 460 g. ISPs may operate or subscribe to services that provide 461 'sinkholing' or 'honeynet' capabilities. This may enable the ISP 462 to obtain near-real-time lists of bot infected computers as they 463 attempt to join a larger botnet or propagate to other hosts on a 464 network. 466 h. ISP industry associations should examine the possiblity of 467 collating statistics from ISP members in order to provide good 468 statistics about bot infections based on real ISP data. 470 i. An Intrusion Detection System(IDS) can be a useful tool to 471 actually identify to help identify the malware. An IDS tool such 472 as SNORT (open source IDS platform) can be placed in a Walleed 473 Garden and used to analyse end user traffic to confirm malware 474 type. This will help with remediation of the infected device. 476 6. Notification to Internet Users 478 Once an ISP has detected a bot, or the strong likelihood of a bot, 479 steps should be undertaken to inform the Internet user that they may 480 have a bot-related problem. Depending upon a range of factors, from 481 the technical capabilities of the ISP, to the technical attributes of 482 their network, financial considerations, available server resources, 483 available organizational resources, the number of likely infected 484 computers detected at any given time, and the severity of any 485 possible threats, among many other things, an ISP should decide the 486 most appropriate method or methods for providing notification to one 487 or more of their customers or Internet users. Such notification 488 methods may include one or more of the following, as well as other 489 possible methods not described below 491 It is important to note that none of these methods are guaranteed to 492 be successful, and that each has its own set of limitations. In 493 addition, in some cases, an ISP may determine that a combination of 494 two or more methods is most appropriate. Finally, notification is 495 also considered time sensitive; if the user does not receive or view 496 the notification or a timely basis, then a particular bot could 497 launch an attack, exploit the user, or cause other harm. If 498 possible, an ISP should establish a preferred means of communication 499 when the subscriber first signs up for service. As a part of the 500 notification process, ISPs should maintain a record of the allocation 501 of IP addresses to subscribers for such a period as allows any bot 502 detection technology to be accurately able to link an infected IP 503 address to a subscriber. This record should only be maintained for a 504 period of time which is necessary, in order to maintain the 505 protection of the privacy of an individual subscriber. 507 One important factor to bear in mind is that notification to end 508 users needs to be defended against spoofing by third parties. This 509 must be done to protect against the possibility of notifications 510 being spoofed and used by bots to deliver additional malware. 512 6.1. Email Notification 514 This is probably the most common form of notification used by ISPs. 515 One drawback of using email is that it is not guaranteed to be viewed 516 within a reasonable time frame, if at all. The user may be using a 517 different primary email address than that which they have provided to 518 the ISP. In addition, some ISPs do not provide an email account at 519 all, as part of a bundle of Internet services, and/or do not have a 520 need for or method in which to request or retain the primary email 521 addresses of Internet users of their networks. Another possibility 522 is that the user, their email client, and/or their email servers 523 could determine or classify such a notification as spam, which could 524 delete the message or otherwise file it in an email folder that the 525 user may not check on a regular and/or timely basis. Bot masters 526 have also been known to impersonate the ISP or trusted sender and 527 send fradulant emails to the users. This technique of solical 528 engineering, generally referred to as 'phishing', often leads to new 529 bot infestations. Finally if the user's email credentials are 530 compromised, then a hacker and/or a bot could simply login to the 531 user's email account and delete the email before it is read by the 532 user. 534 6.2. Telephone Call Notification 536 A telephone call may be an effective means of communication in 537 particularly high-risk situations. However, telephone calls may not 538 be feasible due to the cost of making a large number of calls, as 539 measured in either time, money, organizational resources, server 540 resources, or some other means. In addition, there is no guarantee 541 that the user will answer their phone. To the extent that the 542 telephone number called by the ISP can be answered by the infected 543 computing device, the bot on that computer may be able to disconnect, 544 divert, or otherwise interfere with an incoming call. Users may also 545 interpret such a telephone notification as a telemarketing call and 546 as such not welcome it, or not accept the call at all. Finally, even 547 if a representative of the ISP is able to connect with and speak to a 548 user, that user is very likely to lack the necessary technical 549 expertise to understand or be able to effectively deal with the 550 threat. 552 6.3. Postal Mail Notification 554 This form of notification is probably the least popular and effective 555 means of communication, due to both preparation time, delivery time, 556 the cost of printing and paper, and the cost of postage. 558 6.4. Walled Garden Notification 560 Placing a user in a walled garden is another approach that ISPs may 561 take to notify users. A walled garden refers to an environment that 562 controls the information and services that a subscriber is allowed to 563 utilize and what network access permissions are granted. This is an 564 effective technique because it could be able to block all 565 communication between the bot and the command and control channel, 566 which may impair the ability of a bot to disrupt or block attempts to 567 notify the user. 569 While in many cases the user is almost guaranteed to view the 570 notification message and take any appropriate remediation actions, 571 this approach poses can pose other challenges. For example, it is 572 not always the case that a user is actively using a computer that 573 uses a web browser or which has a web browser actively running on it. 574 In one example, a user could be playing a game online, via the use of 575 a dedicated, Internet-connected game console. In another example, 576 the user may not be using a computer with a web browser when they are 577 placed in the walled garden and may instead be in the course of a 578 telephone conversation, or may be expecting to receive a call, using 579 a Voice Over IP (VoIP) device of some type. As a result, the ISP may 580 feel the need to maintain a potentially lengthy white list of domains 581 which are not subject to the typical restrictions of a walled garden, 582 which could well prove to be an onerous task, from an operational 583 perspective. 585 The ISP has several options to determine when to let the user out of 586 the walled garden. One approach may be to let the user determine 587 when to exit. This option is suggested when the purpose of the 588 walled garden is to notify users and provide information on 589 remediation only, particularly since notification is not a guarantee 590 of successful remediation. It could also be the case that, for 591 whatever reason, the user makes the judgment that they cannot then 592 take the time to remediate their computer and that other online 593 activities which they would like to resume are more important. Exit 594 from the walled garden may also involve a process to verify that it 595 is indeed the user who is requesting exit from the walled garden and 596 not the bot. 598 Once the user acknowledges the notification, then the user decides to 599 either remediate and then exit the walled garden, or exit the walled 600 garden without addressing the issue. Another approach may be to 601 enforce a stricter policy and require the user to clean the computer 602 prior to permitting the user to exit the walled garden, though this 603 may not be technically feasible depending upon the type of bot, 604 obfuscation techniques employed by a bot, and/or a range of other 605 factors. Thus, the ISP may also need to support tools to scan the 606 infected computer and determine whether it is still infected or rely 607 on user judgment that the bot has been disabled or removed. One 608 challenge with this approach is that if the user has multiple 609 computers sharing a single IP address, such as via a common home 610 gateway device which performs Network Address Translation (NAT). In 611 such a case, the ISP may need to determine from user feedback, or 612 other means, that all affected computers have been remediated, which 613 may or may not be technically feasible. 615 Finally, when a walled garden is used, a list of well-known addresses 616 for both operating system vendors and security vendors should be 617 created and maintained in a white list which permits access to these 618 sites. This can be important for allowing access from the walled 619 garden by end users in search of operating system and application 620 patches. 622 6.5. Instant Message Notification 624 Instant messaging provides the ISP with a simple means to communicate 625 with the user. There are several advantages to using IM which makes 626 it an attractive option. If the ISP provides IM service and the user 627 subscribes to it, then the user can be notified easily. IM-based 628 notification can be a cost effective means to communicate with users 629 automatically from an IM alert system or via a manual process, by the 630 ISP's support staff. Ideally, the ISP should allow the user to 631 register their IM identity in an ISP account management system and 632 grant permission to be contacted via this means. If the IM service 633 provider supports off-line messaging, then the user can be notified 634 regardless of whether they are currently logged into the IM system. 636 There are several drawbacks with this communications method. There 637 is a high probability that subscriber may interpret the communication 638 to be spam, and as such ignore it. Also, not every user uses IM 639 and/or the user may not provide their IM identity to the ISP so some 640 alternative means have to be used. Even in those cases where a user 641 does have an IM address, they may not be signed onto that IM system 642 when the notification is attempted. There maybe also be a privacy 643 concern on the part of users, when such an IM notification must be 644 transmitted over a third-party network and/or IM service. As such, 645 should this method be used, the notification should be discreet and 646 not include any PII in the notification itself. 648 6.6. Short Message Service (SMS) Notification 650 SMS allows the ISP send a brief description of the problem to notify 651 the user of the issue, typically to a mobile device such as a mobile 652 phone or smart phone. Ideally, the ISP should allow the user to 653 register their mobile number and/or SMS address in an ISP account 654 management system and grant permission to be contacted via this 655 means. The primary advantage of SMS is that users are familiar with 656 receiving text messages and are likely to read them. However, users 657 may not act on the notification immediately if they are not in front 658 of their computer system at the time of the SMS notification. 660 One disadvantage is that ISPs may have to follow up with an alternate 661 means of notification if not all of the necessary information maybe 662 conveyed in one message, given constraints on the number of 663 characters in an individual message (typically 140 characters). 664 Another disadvantage with SMS is the cost associated with it. The 665 ISP has to either build its own SMS gateway to interface with the 666 various wireless network service providers or use a third-party SMS 667 clearinghouse (relay) to notify users. In both cases, an ISP will 668 typically pay on a per-message basis to send SMS notifications. An 669 additional downside is that SMS messages sent to a user may result in 670 a charge to the user by their wireless provider, depending upon the 671 plat to which they subscribe. Another minor disadvantage is that it 672 is possible to notify the wrong user if the intended user changes 673 their mobile number but forgets to update it with the ISP. 675 There are several other drawbacks with this communications method. 676 There is a high probability that subscriber may interpret the 677 communication to be spam, and as such ignore it. Also, not every 678 user uses SMS and/or the user may not provide their SMS address or 679 mobile number to the ISP. Even in those cases where a user does have 680 an SMS address or mobile number, their device may not be powered on 681 or otherwise available on a wireless network when the notification is 682 attempted. There maybe also be a privacy concern on the part of 683 users, when such an SMS notification must be transmitted over a 684 third-party network and/or SMS clearinghouse. As such, should this 685 method be used, the notification should be discreet and not include 686 any PII in the notification itself. 688 6.7. Web Browser Notification 690 Near real-time notification to the user's web browser is another 691 technique that may be utilized for notifying the user, though how 692 such a system might operate is outside the scope of this document. 693 Such a notification could have a comparative advantage over a walled 694 garden notification, in that it does not restrict traffic to a 695 specified list of destinations in the same way that a walled garden 696 by definition would. However, as with a walled garden notification, 697 there is no guarantee that a user is at any given time making use of 698 a web browser, though such a system could certainly provide a 699 notification when such a browser is eventually used. Compared to a 700 walled garden, a web browser notification is probably preferred from 701 the perspective of Internet users, as it does not have the risk of 702 disrupting non-web sessions, such as online games, VoIP calls, etc. 703 (as noted in Section 6.4). 705 6.8. Considerations for Notification to Public Network Locations 707 Delivering a notification to a location that provides a shared public 708 network, such as a train station, public square, coffee shop, or 709 similar location may be of low value since the users connecting to 710 such networks are typically highly transient and generally not know 711 to site or network administrators. For example, a system may detect 712 that a computer on such a network has a bot, but by the time a 713 notification is generated that user has departed from the network and 714 moved elsewhere. 716 6.9. Considerations for Notification to Network Locations Using a 717 Shared IP Address 719 Delivering a notification to a location that Internet access routed 720 through one or more shared public IP addresses may be of low value 721 since it may be quite difficult to differentiate between users when 722 providing a notification. For example, on a business network of 500 723 users, all sharing one public IP address, it may be sub-optimal to 724 provide a notification to all 500 users if you only need one specific 725 user to be notified and take action. As a result, such networks may 726 find value in establishing a localized bot detection and notification 727 system, just as they are likely to also establish other localized 728 systems for security, file sharing, email, and so on. 730 7. Remediation of Compters Infected with a Bot 732 This section covers the different options available to remediate a 733 computer, which means to remove, disable, or otherwise render a bot 734 harmless. Prior to this step, an ISP has detected the bot, notified 735 the user that one of their computers is infected with a bot, and now 736 may provide some recommended means to clean the computer. The 737 generally recommended approach is to provide the necessary tools and 738 education to the user so that they may perform bot remediation 739 themselves, particularly given the risks and difficulties inherent in 740 attempting to remove a bot. 742 For example, this may include the creation of a special web site with 743 security-oriented content that is dedicated for this purpose. This 744 should be a well-publicized security web site to which a user with a 745 bot infection can be directed to for remediation. This security web 746 site should clearly explain why the user was notified and may include 747 an explanation of what bots are, and the threats that they pose. 748 There should be a clear explanation of the steps that the user should 749 take in order to attempt to clean their computer and provide 750 information on how users can keep the computer free of future 751 infections. The security web site should also have a guided process 752 that takes non-technical users through the remediation process, on an 753 easily understood, step-by-step basis. 755 In terms of the text used to explain what bots are and the threats 756 that they pose, something simple such as this may suffice: 758 "What is a bot? A bot is a piece of software, generally 759 installed on your machine without your knowledge, which either 760 sends spam or tries to steal your personal information. They 761 can be very difficult to spot, though you may have noticed that 762 your computer is running much more slowly than usual or you 763 notice regular disk activity even when you are not doing 764 anything. Ignoring this problem is not really an option since 765 your personal information is currently at risk. Thus, bots 766 need to be removed to protect your data and your personal 767 information." 769 It is also important to note that it may not be immediately apparent 770 to the Internet user precisely which devices have been infected with 771 a particular bot. This may be due to the user's home network 772 configuration, which may encompass several computers, where a home 773 gateway which performs Network Address Translation (NAT) to share a 774 single public IP address has been used. Therefore, any of these 775 devices can be infected with a bot. The consequence of this for an 776 ISP is that remediation advice may not ultimately be immediately 777 actionable by the Internet user, as that user may need to perform 778 additional investigation within their own home network. 780 An added complication is that the user may have a bot infection on a 781 device such as a video console, multimedia system, appliance, or 782 other end-user computing device which does not have a typical Windows 783 or Macintosh user interface. As a result, diligence needs to be 784 taken by the ISP where possible such that they can identify and 785 communicate the specific nature of the device that has been infected 786 with a bot, and further providing appropriate remediation advice. 788 There are a number of forums that exist online to provide security 789 related support to end users. These forums are staffed by volunteers 790 and often are focussed around the use of a common tool set to help 791 end users to remediate computers infected with malware. It may be 792 advantageous to ISPs to foster a relationship with one or more 793 forums, perhaps by offering free hosting or other forms of 794 sponsorship. 796 8. Guided Remediation Process 798 Minimally the Guided Remediation Process should include options 799 and/or recommendations on how a user should: 801 1. Backup personal Documents, for example: "Before you start, make 802 sure to back up all of your important data. (You should do this 803 on a regular basis anyway.) You can back up your files manually 804 or using a system back-up software utility, which may be part of 805 your Operating System (OS). You can back your files up to a USB 806 Thumb Drive (aka USB Key), a writeable CD/DVD-ROM, an external 807 hard drive, or a network file server." 809 2. Download OS patches and Anti-Virus (A/V) software updates. For 810 example, links could be provided to Microsoft Windows updates at 811 http://update.microsoft.com/microsoftupdate/v6/ 812 default.aspx?ln=en-us as well as to Apple MacOS updates at 813 http://support.apple.com/kb/HT1338?viewlocale=en_US. 815 3. Explain how to configure the computer to automatically install 816 updates for the OS, A/V and other common Web Browsers such as 817 Microsoft Internet Explorer, Mozilla Firefox, Apple Safari, 818 Opera, and Google Chrome. 820 4. The flow should also have the option for users to get 821 professional assistance if they are unable to remove the bots 822 themselves. If purchasing third party assistance, then the user 823 should be encouraged to pre-determine how much they are willing 824 to pay for that help. If the computer that is being remediated 825 is old and can easily be replaced with a new, faster, larger and 826 more reliable system for three or four hundred dollars, the it 827 makes no sense to spend five or six hundred dollars to fix the 828 old computer, for example. On the other hand, if the customer 829 has a brand new computer that cost several thousand dollars, it 830 might make perfect sense to spend the money in attempting to 831 remediate it. 833 5. To continue, regardless of whether the user or a knowledgeable 834 technical assistant is working on remediating the computer, their 835 first task should be to determine which of multiple potentially- 836 infected machines may be the one that needs attention (in the 837 common case of multiple computers in a home network). Sometimes, 838 as in cases where there is only a single directly-attached 839 computer, or the user has been noticing problems with one of 840 their computers, this can be easy. Other times, it may be more 841 difficult. If the user is behind a home gateway/router, then the 842 first task may be to ascertain which of the machines is infected. 843 In some cases the user may have to check all machines to identify 844 the infected one. 846 6. User surveys to solicit feedback on whether the notification and 847 remediation process is effective and what recommended changes 848 could be made in order to improve the ease, understandability, 849 and effectiveness the remediation process. 851 7. If the user is interested in reporting his or her computer's bot 852 infection to an applicable law enforcement authority, then the 853 computer effectively becomes a cyber "crime scene" and should not 854 be mitigated unless or until law enforcement has collected the 855 necessary evidence. For individuals in this situation, the ISP 856 should refer them to local, state, federal, or other relevant 857 computer crime offices. (Note: Some "minor" incidents, even if 858 highly traumatic to the user, may not be sufficiently serious for 859 law enforcement to commit some of their limited resources to an 860 investigation.) 862 9. Professionally-Assisted Remediation Process 864 It should be acknowledged that, based on the current state of 865 remediation tools and the technical abilities of end users, that many 866 users may be unable to remediate on their own. As a result, it is 867 recommended that users have the option to avail themselves of 868 professional assistance. This may entail online or telephone 869 assistance for remediation, as well as working face to face with a 870 professional who has training and expertise in the removal of 871 malware. 873 10. Security Considerations 875 This document describes in detail the numerous security risks and 876 concerns relating to bot nets. As such, it has been appropriate to 877 include specific information about security in each section above. 878 This document describes the security risks related to malicious bot 879 infections themselves, such as enabling identity theft, theft of 880 authentication credentials, and the use of a computer to unwittingly 881 participate in a DDoS attack, among many other risks. This document 882 also describes at a high level the activities that ISPs should be 883 sensitive to, where the collection or communication of PII may be 884 possible. Finally, the document also describes security risks which 885 may relate to the particular methods of communicating a notification 886 to Internet users. Bot networks and bot infections pose extremely 887 serious security risks and any reader should review this document 888 carefully. 890 In addition, regarding notifications, as described in the Section 6, 891 care should be taken to assure users that notifications have been 892 provided by a trustworthy site and/or party, so that the notification 893 is more difficult for phishers to mimic, or that the user has some 894 level of trust that the notification is valid, and/or that the user 895 has some way to verify via some other mechanism or step that the 896 notification is valid. 898 11. IANA Considerations 900 There are no IANA considerations in this document. 902 12. Acknowledgements 904 The authors wish to acknowledge the following individuals and 905 organisations for their review and feedback of this document: 907 Jonathan Curtis 909 Jeff Chan 911 Roland Dobbins 913 Eliot Gillum 915 Joel Halpern 917 The Messaging Anti-Abuse Working Group (MAAWG) 919 Jose Nazario 921 Gunter Ollmann 923 Joe Stewart 925 Eric Ziegast 927 13. Informative references 929 [Battling Botnets and Online Mobs: Estonia's Defense Efforts during 930 the Internet War] 931 Evron, G., "Battling Botnets and Online Mobs: Estonia's 932 Defense Efforts during the Internet War", May 2005, . 938 [Case Study: How a Bookmaker and a Whiz Kid Took On a DDOS-based 939 Online Extortion Attack] 940 Berinato, S., "Case Study: How a Bookmaker and a Whiz Kid 941 Took On a DDOS-based Online Extortion Attack", May 2005, < 942 http://www.csoonline.com/article/220336/ 943 How_a_Bookmaker_and_a_Whiz_Kid_Took_On_a_DDOS_based_Online 944 _Extortion_Attack>. 946 [Cyberspace as a Combat Zone: The Phenomenon of Electronic Jihad] 947 Alshech, E., "Cyberspace as a Combat Zone: The Phenomenon 948 of Electronic Jihad", February 2007, . 951 [Emerging Cyber Threats Report for 2009: Data, Mobility and Questions 952 of Responsibility will Drive Cyber Threats in 2009 and Beyond] 953 Ahamad, M., Amster, D., Barret, M., Cross, T., Heron, G., 954 Jackson, D., King, J., Lee, W., Naraine, R., Ollman, G., 955 Ramsey, J., Schmidt, H., and P. Traynor, "Emerging Cyber 956 Threats Report for 2009: Data, Mobility and Questions of 957 Responsibility will Drive Cyber Threats in 2009 and 958 Beyond", October 2008, . 961 [RFC1459] Oikarinen, J. and D. Reed, "Internet Relay Chat Protocol", 962 RFC 1459, May 1993. 964 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 965 Requirement Levels", BCP 14, RFC 2119, March 1997. 967 [RFC2142] Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND 968 FUNCTIONS", RFC 2142, May 1997. 970 [RFC3954] Claise, B., "Cisco Systems NetFlow Services Export Version 971 9", RFC 3954, October 2004. 973 [Spamalytics: An Empirical Analysis of Spam Marketing Conversion] 974 Kanich, C., Kreibich, C., Levchenko, K., Enright, B., 975 Voelker, G., Paxson, V., and S. Savage, "Spamalytics: An 976 Empirical Analysis of Spam Marketing Conversion", 977 October 2008, . 980 [The Gh0st in the Shell: Network Security in the Himalayas] 981 Vallentin, M., Whiteaker, J., and Y. Ben-David, "The Gh0st 982 in the Shell: Network Security in the Himalayas", 983 February 2010, . 986 [The snooping dragon: social-malware surveillance of the Tibetan 987 movement] 988 Nagaraja, S. and R. Anderson, "The snooping dragon: 989 social-malware surveillance of the Tibetan movement", 990 March 2009, 991 . 993 Appendix A. Document Change Log 995 [RFC Editor: This section is to be removed before publication] 996 -04 version: 998 o Minor tweaks made by Jason - ready for wider review and next 999 steps. Also cleared open issues. Lastly, added 2nd paragraph to 1000 security section and added sections on limitations relating to 1001 public and other shared network sites. Added a new section on 1002 professional remediation. 1004 -04 version: 1006 o Updated reference to BIOS based malware, added wording on PII and 1007 local jurisdictions, added suggestion that industry body produce 1008 bot stats, added suggestion that ISPs use volunteer forums 1010 -03 version: 1012 o all updates from Jason - now ready for wider external review 1014 -02 version: 1016 o all updates from Jason - still some open issues but we're now at a 1017 place where we can solicit more external feedback 1019 -01 version: 1021 o -01 version published 1023 Appendix B. Open Issues 1025 [RFC Editor: This section is to be removed before publication] 1027 None at this time 1029 Authors' Addresses 1031 Jason Livingood 1032 Comcast Cable Communications 1033 One Comcast Center 1034 1701 John F. Kennedy Boulevard 1035 Philadelphia, PA 19103 1036 US 1038 Email: jason_livingood@cable.comcast.com 1039 URI: http://www.comcast.com 1040 Nirmal Mody 1041 Comcast Cable Communications 1042 One Comcast Center 1043 1701 John F. Kennedy Boulevard 1044 Philadelphia, PA 19103 1045 US 1047 Email: nirmal_mody@cable.comcast.com 1048 URI: http://www.comcast.com 1050 Mike O'Reirdan 1051 Comcast Cable Communications 1052 One Comcast Center 1053 1701 John F. Kennedy Boulevard 1054 Philadelphia, PA 19103 1055 US 1057 Email: michael_oreirdan@cable.comcast.com 1058 URI: http://www.comcast.com