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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 12, 2010 Comcast 6 February 8, 2010 8 Recommendations for the Remediation of Bots in ISP Networks 9 draft-oreirdan-mody-bot-remediation-04 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 12, 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 . . . . . . . . . . . . . . . . . . . . . . 7 84 6. Notification to Internet Users . . . . . . . . . . . . . . . . 11 85 7. Remediation of Compters Infected with a Bot . . . . . . . . . 16 86 8. Guided Remediation Process . . . . . . . . . . . . . . . . . . 17 87 9. Security Considerations . . . . . . . . . . . . . . . . . . . 19 88 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 89 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19 90 12. Informative references . . . . . . . . . . . . . . . . . . . . 20 91 Appendix A. Document Change Log . . . . . . . . . . . . . . . . . 20 92 Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . . 20 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 95 1. Requirements Language 97 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 98 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 99 document are to be interpreted as described in [RFC2119]. 101 2. Key Terminology 103 This section defines the key terms used in this document. 105 2.1. Malicious Bots, or Bots 107 A malicious "bot" (derived from the word "robot", hereafter simply 108 referred to as a "bot") refers to a program that is surreptitiously 109 installed on a system in order to enable that system to automatically 110 (or semi-automatically) perform a task or set of tasks typically 111 under the command and control of a remote administrator, or "bot 112 master." Bots are also known as "zombies". It is important to note 113 that there are 'good', or benign bots. Such benign bots are often 114 found in such environments such as gaming and Internet Relay Chat 115 (IRC) [RFC1459], where a continual, interactive presence can be a 116 requirement for participating in the games, interacting with a 117 computing resource, or other purposes. 119 However, for the purposes of this document, all mention of bots 120 should assume that the bots involved are malicious in nature. Such 121 malicious bots shall generally be assumed to have been deployed 122 without the permission or conscious understanding of a particular 123 Internet user. Thus, without a user's knowledge, bots may transform 124 the user's computing device into a platform from which malicious 125 activities can be conducted. 127 2.2. Bot Networks, or Botnets 129 These are defined as concerted networks of bots capable of acting on 130 instructions generated remotely. The malicious activities are either 131 focused on the information on the local machine or acting to provide 132 services for remote machines. Bots are highly customizable so they 133 can be programmed to do many things. The major malicious activities 134 include: identity theft, spam, distributed denial of service (DDoS) 135 attacks, key-logging, fraudulent DNS (pharming), proxy services, fast 136 flux hosting and click fraud. 138 Infection vectors include un-patched operating systems, software 139 vulnerabilities, weak/non-existent passwords, malicious websites, un- 140 patched browsers, malware, vulnerable helper applications and social 141 engineering techniques to gain access to the user's computer. The 142 detection and destruction of bots is an ongoing issue and also a 143 constant battle between the internet security community, network 144 security engineers and bot developers. 146 Initially, bots used IRC to communicate but were easy to shutdown if 147 the command and control server was identified and deactivated. Newer 148 command and control methods have evolved, such that those currently 149 employed by bot masters make them much more resistant to 150 deactivation. With the introduction of P2P, HTTP and other resilient 151 communication protocols along with the widespread adoption of 152 encryption, bots are considerably more difficult to identify and 153 isolate from typical network usage. As a result increased reliance 154 is being placed on anonmaly detection and behavioral analysis, both 155 locally and remotely, to identify bots. 157 2.3. Computer 159 A computer, as used in the context of this document, is intended to 160 refer to a computing device that connects to the Internet. This 161 encompasses devices used by Internet users such as personal 162 computers, including laptops, desktops, and netbooks, as well as 163 mobile phones, smart phones, home gateway devices, and other end user 164 computing devices which are connected or can connect to the public 165 Internet and/or private IP networks. 167 Increasingly, other household systems and devices contain embedded 168 computers which are connected to or can connect to the public 169 Internet and/or private IP networks. However, these devices may not 170 be under interactive control of the Internet user, such as may be the 171 case with various smart home and smart grid devices. 173 2.4. Malware 175 This is short for malicious software. In this case, malicious bots 176 are considered a subset of malware. Other forms of malware could 177 include viruses and other similar types of software. Internet users 178 can sometimes cause their computer to be infected with malware, which 179 may include a bot or cause a bot to install itself, via inadvertently 180 accessing a specific website, downloading a specific file, or other 181 activities. 183 Alternatively, Internet-connected computers may become infected with 184 malware through externally initiated malicious activities such as the 185 exploitation of vulnerabilities or the brute force guessing of access 186 credentials. 188 3. Introduction and Problem Statement 190 Computers used by Internet users, which in this case are customers of 191 an Internet Service Provider (ISP), can be infected with malware 192 which may contain and/or install one or more bots on a computer. 193 This can present a major problem for an ISP for a number of reasons 194 (not to mention of course the problems created for users). First, 195 these bots can be used to send spam, in some cases very large volumes 196 of spam. This spam can result in extra cost for the ISPs in terms of 197 wasted network, server, and/or personnel resources, among many other 198 potential costs and side effects. Such spam can also negatively 199 affect the reputation of the ISP, their customers, and the email 200 reputation of the IP address space used by the ISP (often referred to 201 simply as 'IP reputation'). 203 In addition, these bots can act as platforms for directing, 204 participating in, or otherwise conducting attacks on critical 205 Internet infrastructure. Bots are frequently used as part of 206 concerted Distributed Denial of Service (DDoS) attacks for criminal, 207 political or other motivations. For example, bots have been used to 208 attack Internet resources and infrastructure ranging from web sites, 209 to email servers and DNS servers, as well as the critical Internet 210 infrastructure of entire countries. Motivations for such coordinated 211 DDoS attacks can range from criminal extortion attempts through to 212 online protesting and nationalistic fervor. 214 While any computing device can be infected with bots, the majority of 215 bot infections affect the personal computers used by Internet end 216 users. As a result of the role of ISPs in providing IP connectivity, 217 among many other services, to Internet users, these ISPs are in a 218 unique position to be able to attempt to detect and observe bot nets 219 operating in their networks. Furthermore, ISPs may also be in a 220 unique position to be able to communicate to Internet users which are 221 their customers, when customers' computers may have been determined 222 to have been or possibly have been infected with one or more bots. 224 From an end user perspective, knowing that their computer has been 225 infected with one or more bots is very important information. Once 226 they know this, they can take steps to remove the bot, protect 227 themselves in the future, and resolve any problems which may stem 228 from the bot infection. Given that bots can drain local computing 229 and network resources, enable theft of personal information 230 (including personal financial information), enable the computer to be 231 used from criminal activities (that may result in the Internet user 232 being legally culpable), destroy or leave the PC in an unrecoverable 233 state via 'kill switch' bot technologies, it is important to notify 234 the user that they may be infected with a bot. 236 As a result, the intent of this document is to provide a guide to 237 ISPs and other organizations for the remediation of these computers 238 infected with bots, so as to reduce the size of bot nets and minimize 239 the potential harm that bots can inflict upon Internet infrastructure 240 generally, as well as on individual Internet users. Efforts by ISPs 241 and other organizations could therefore, over time, reduce the pool 242 of computers infected with bots on the Internet, which in turn could 243 result in smaller bot nets with less capability for disruption. 245 The potential mitigation of bots is accomplished through a process of 246 detection, notification to Internet users, and remediation of that 247 bot with a variety of tools, as described later in this document. 249 4. Important Notice of Limitations and Scope 251 The techniques described in this document in no way guarantee the 252 remediation of all bots. Bot removal is potentially a task requiring 253 specialized knowledge, skills and tools, and may be beyond the 254 ability of average users. Attempts at bot removal may frequently be 255 unsuccessful, or only partially successful, and may leave a user's 256 system in an unstable and unsatisfactory state or even in a state 257 where it is still infected. Attempts at bot removal can also result 258 in side effects ranging from a loss of data or other files, all the 259 way through partial or complete loss of system usability. 261 In general, the only way a user can be sure they have removed some of 262 today's increasingly sophisticated malware is by 'nuking-and-paving' 263 the system: reformatting the drive, reinstalling the operating system 264 and applications (including all patches) from scratch, and then 265 restoring user files from a clean backup. However the introduction 266 of BIOS-based malware may mean that, in some cases, this will not be 267 enough and may prove to be more than any end user can be reasonably 268 expected to resolve. Experienced users would have to reflash BIOS in 269 their machines in order to remove BIOS-based malware. 271 Devices with embedded operating systems, such as video gaming 272 consoles and smart home appliances, will most likely be beyond a 273 user's capability to remediate by themselves, and will typically 274 require the aid of vendor-specific advice, updates and tools. Care 275 must be taken when imparting remediation advice to Internet users 276 given the increasingly wide array of computing devices that can be, 277 or could be, infected by bots in the future. 279 5. Detection of Bots 281 An ISP must first identify that an Internet user, in this case a user 282 that is assumed to be their customer or otherwise connected to the 283 ISP's network, is determined to be infected, or likely to have been 284 infected with a bot. The ISP should attempt to detect the presence 285 of bots using methods, processes, and tools which maintain the 286 privacy of the personally identifiable information (PII) of their 287 customers. The ISP also should not block legitimate traffic in the 288 course of bot detection, and should instead employ detection methods, 289 tools, and processes which seek to be non-disruptive, as well as 290 being transparent to Internet users and end-user applications. 292 Detection methods, tools, and processes may include things such as 293 analysis of specific network and/or application traffic flows (such 294 as traffic to an email server), analysis of aggregate network and/or 295 application traffic data, data feeds received from other ISPs and 296 organizations (such as lists of the ISP's IP addresses which have 297 been reported to have sent spam), feedback from the ISP's customers 298 or other Internet users, as well as a wide variety of other 299 possibilities. It is likely that a combination of multiple bot 300 detection data points will prove to be an effective approach in order 301 to corroborate information of varying dependability or consistency, 302 as well as to avoid or minimize the possibility of false positive 303 identification of computers. Detection should also, where possible 304 and feasible, attempt to classify a bot in order to confirm that it 305 is malicious in nature, estimate the variety and severity of threats 306 it may pose (such as spam bot, key-logging bot, file distribution 307 bot, etc.), and to determine potential methods for eventual 308 remediation. However, given the dynamic nature of botnet management 309 and the criminal incentives to seek quick financial rewards, botnets 310 frequently update or change their core malicious capabilities. As a 311 consequence, botnets that are initially detected and classified by 312 the ISP as one particular type of bot need to be continuously 313 monitored and tracked in order to correctly identify the threat they 314 pose at any particular point in time. 316 Detection is also time-sensitive. If complex analysis is required 317 and multiple confirmations are needed to confirm a bot is indeed 318 present, then it is possible that the bot may cause some damage (to 319 either the infected computer or a remotely targeted system) before it 320 can be stopped. This may mean that an ISP may need to balance the 321 desire or need to definitively classify and/or confirm a bot, which 322 may take an extended period of time, with the ability to predict the 323 strong likelihood of a bot in a very short period of time. This 324 'definitive-vs-likely' challenge is difficult and, when in doubt, 325 ISPs should probably err on the side of caution by communicating when 326 a likely bot infection has taken place. This also means that 327 Internet users may benefit from the deployment of client-based 328 software protections or other software tools, which can enable rapid 329 performance of heuristically-based detection bot activity, such as 330 the detection of a bot as it starts to communicate a bot net and 331 execute some type of command. Any bot detection systems should also 332 be capable of learning and adapting, either via manual intervention 333 or automatically, in order to cope with a rapidly evolving threat. 335 As noted above, detection methods, tools, and processes should ensure 336 that privacy of customers' PII is maintained. While bot detection 337 methods, tools, and processes are similar to spam and virus defenses 338 deployed by the ISP for the benefit of their customers (and may be 339 directly related to those defenses), attempts to detect bots should 340 take into account the need of an ISP to take care to ensure any PII 341 collected or incidentally detected is properly protected. The 342 definition of PII varies from one jurisdiction to the next so proper 343 care must be taken to ensure that any actions taken comply with 344 legislation and good practice in the jurisdiction in which the PII is 345 gathered. Finally, depending upon the geographic region within which 346 an ISP operates, certain methods relating to bot detection may need 347 to be included in relevant terms of service documents or other 348 documents which are available to the customers of a particular ISP. 350 There are several bot detection methods, tools, and processes that an 351 ISP may choose to utilize, as noted in the list below. It is 352 important to note that the technical solutions available are 353 relatively immature, and are likely to change over time, evolving 354 rapidly in the coming years. While these items are described in 355 relation to ISPs, they may also be applicable to organizations 356 operating other networks, such as campus networks and enterprise 357 networks. 359 a. Where legally permissible or otherwise an industry accepted 360 practice in a particular market region, an ISP may in some manner 361 "scan" their IP space in order to detect un-patched or otherwise 362 vulnerable hosts. This may provide the ISP with the opportunity 363 to easily identify Internet users who appear to already be or are 364 at great risk of being infected with a bot. ISP's should note 365 that some types of port scanning may leave network services in a 366 hung state or render them unusable due to common frailties, and 367 that many modern firewall and host-based intrusion detection 368 implementations may alert the Internet user to the scan. As a 369 result the scan may be interpreted as a malicious attack against 370 the computer. Vulnerability scanning has a higher probability of 371 leaving accessible network services and applications in a damaged 372 state and will often result in a higher probability of detection 373 by the Internet user and subsequent interpretation as a targeted 374 attack. Depending upon the vulnerability being scanned, some 375 automated methods of vulnerability checking may result in data 376 being altered or created afresh on the Internet users computer 377 which be a problem in many legal environments. 379 b. An ISP may also communicate and share selected data, via feedback 380 loops or other mechanisms, with various third parties. Feedback 381 loops are consistently formatted feeds of real-time (or nearly 382 real-time) abuse reports offered by threat data clearinghouses, 383 security alert organizations, other ISPs, and other 384 organizations. The data may include, but is not limited to, 385 lists of the IP addresses computers which have or are likely to 386 have a bot running, domain names or fully qualified domain names 387 (FQDNs) known to host malware and/or be involved in the command 388 and control of botnets, IP addresses know to host malware and/or 389 be involved in the command and control of botnets, recently 390 tested or discovered techniques or detecting or remediating bot 391 infections, new threat vectors, and other relevant information. 392 Good examples of this include SNDS from Microsoft, XBL and PBL 393 from Spamhaus and the DSHIELD AS tool from the SANS Institue. 395 c. An ISP may use Netflow [RFC3954] or other similar passive network 396 monitoring to identify network anomalies that may be indicative 397 of botnet attacks or bot communications. For example, an ISP may 398 be able to identify compromised hosts by identifying traffic 399 destined to IP addresses associated with the command and control 400 of botnets. In addition, bots can be idenfied when a remote host 401 is under a DDoS attack because computers participating in the 402 attack will likely be infected by a bot, frequently as observed 403 at network borders. 405 d. An ISP may use DNS-based techniques to perform detection. For 406 example, a given classified bot may be known to query a specific 407 list of domain names at specific times or on specific dates (in 408 the example of the so-called "Conficker" bot), often by matching 409 DNS queries to a well known list of domains associated with 410 malware. In many cases such lists are distributed by or shared 411 using third parties, such as threat data clearinghouses. 413 e. User complaints: Because hosts infected by bots are frequently 414 used to send spam or participate in DDoS attacks, the ISP 415 servicing those hosts will normally receive complaints about the 416 malicious network traffic. Those complaints may be sent to 417 RFC2142-specified [RFC2142] role accounts, such as abuse@ or 418 postmaster@ or to abuse or security addresses specified by the 419 site as part of its WHOIS (or other) contact data. 421 f. ISPs may also discover likely bot infected hosts located at other 422 sites; when legally permissible or otherwise an industry accepted 423 practice in a particular market region, it may be worthwhile for 424 ISPs to share evidence relating to those compromised hosts with 425 the relevant remote ISP, with security researchers, and with 426 blocklist operators. 428 g. ISPs may operate or subscribe to services that provide 429 'sinkholing' or 'honeynet' capabilities. This may enable the ISP 430 to obtain near-real-time lists of bot infected computers as they 431 attempt to join a larger botnet or propagate to other hosts on a 432 network. 434 h. ISP industry associations should examine the possiblity of 435 collating statistics from ISP members in order to provide good 436 statistics about bot infections based on real ISP data. 438 i. An Intrusion Detection System(IDS) can be a useful tool to 439 actually identify to help identify the malware. An IDS tool such 440 as SNORT (open source IDS platform) can be placed in a Walleed 441 Garden and used to analyse end user traffic to confirm malware 442 type. This will help with remediation of the infected device. 444 6. Notification to Internet Users 446 Once an ISP has detected a bot, or the strong likelihood of a bot, 447 steps should be undertaken to inform the Internet user that they may 448 have a bot-related problem. Depending upon a range of factors, from 449 the technical capabilities of the ISP, to the technical attributes of 450 their network, financial considerations, available server resources, 451 available organizational resources, the number of likely infected 452 computers detected at any given time, and the severity of any 453 possible threats, among many other things, an ISP should decide the 454 most appropriate method or methods for providing notification to one 455 or more of their customers or Internet users. Such notification 456 methods may include one or more of the following, as well as other 457 possible methods not described below 459 It is important to note that none of these methods are guaranteed to 460 be successful, and that each has its own set of limitations. In 461 addition, in some cases, an ISP may determine that a combination of 462 two or more methods is most appropriate. Finally, notification is 463 also considered time sensitive; if the user does not receive or view 464 the notification or a timely basis, then a particular bot could 465 launch an attack, exploit the user, or cause other harm. If 466 possible, an ISP should establish a preferred means of communication 467 when the subscriber first signs up for service. As a part of the 468 notification process, ISPs should maintain a record of the allocation 469 of IP addresses to subscribers for such a period as allows any bot 470 detection technology to be accurately able to link an infected IP 471 address to a subscriber. This record should only be maintained for a 472 period of time which is necessary, in order to maintain the 473 protection of the privacy of an individual subscriber. 475 One important factor to bear in mind is that notification to end 476 users needs to be defended against spoofing by third parties. This 477 must be done to protect against the possibility of notifications 478 being spoofed and used by bots to deliver additional malware. 480 6.1. Email Notification 482 This is probably the most common form of notification used by ISPs. 483 One drawback of using email is that it is not guaranteed to be viewed 484 within a reasonable time frame, if at all. The user may be using a 485 different primary email address than that which they have provided to 486 the ISP. In addition, some ISPs do not provide an email account at 487 all, as part of a bundle of Internet services, and/or do not have a 488 need for or method in which to request or retain the primary email 489 addresses of Internet users of their networks. Another possibility 490 is that the user, their email client, and/or their email servers 491 could determine or classify such a notification as spam, which could 492 delete the message or otherwise file it in an email folder that the 493 user may not check on a regular and/or timely basis. Bot masters 494 have also been known to impersonate the ISP or trusted sender and 495 send fradulant emails to the users. This technique of solical 496 engineering, generally referred to as 'phishing', often leads to new 497 bot infestations. Finally if the user's email credentials are 498 compromised, then a hacker and/or a bot could simply login to the 499 user's email account and delete the email before it is read by the 500 user. 502 6.2. Telephone Call Notification 504 A telephone call may be an effective means of communication in 505 particularly high-risk situations. However, telephone calls may not 506 be feasible due to the cost of making a large number of calls, as 507 measured in either time, money, organizational resources, server 508 resources, or some other means. In addition, there is no guarantee 509 that the user will answer their phone. To the extent that the 510 telephone number called by the ISP can be answered by the infected 511 computing device, the bot on that computer may be able to disconnect, 512 divert, or otherwise interfere with an incoming call. Users may also 513 interpret such a telephone notification as a telemarketing call and 514 as such not welcome it, or not accept the call at all. Finally, even 515 if a representative of the ISP is able to connect with and speak to a 516 user, that user is very likely to lack the necessary technical 517 expertise to understand or be able to effectively deal with the 518 threat. 520 6.3. Postal Mail Notification 522 This form of notification is probably the least popular and effective 523 means of communication, due to both preparation time, delivery time, 524 the cost of printing and paper, and the cost of postage. 526 6.4. Walled Garden Notification 528 Placing a user in a walled garden is another approach that ISPs may 529 take to notify users. A walled garden refers to an environment that 530 controls the information and services that a subscriber is allowed to 531 utilize and what network access permissions are granted. This is an 532 effective technique because it could be able to block all 533 communication between the bot and the command and control channel, 534 which may impair the ability of a bot to disrupt or block attempts to 535 notify the user. 537 While in many cases the user is almost guaranteed to view the 538 notification message and take any appropriate remediation actions, 539 this approach poses can pose other challenges. For example, it is 540 not always the case that a user is actively using a computer that 541 uses a web browser or which has a web browser actively running on it. 542 In one example, a user could be playing a game online, via the use of 543 a dedicated, Internet-connected game console. In another example, 544 the user may not be using a computer with a web browser when they are 545 placed in the walled garden and may instead be in the course of a 546 telephone conversation, or may be expecting to receive a call, using 547 a Voice Over IP (VoIP) device of some type. As a result, the ISP may 548 feel the need to maintain a potentially lengthy white list of domains 549 which are not subject to the typical restrictions of a walled garden, 550 which could well prove to be an onerous task, from an operational 551 perspective. 553 The ISP has several options to determine when to let the user out of 554 the walled garden. One approach may be to let the user determine 555 when to exit. This option is suggested when the purpose of the 556 walled garden is to notify users and provide information on 557 remediation only, particularly since notification is not a guarantee 558 of successful remediation. It could also be the case that, for 559 whatever reason, the user makes the judgment that they cannot then 560 take the time to remediate their computer and that other online 561 activities which they would like to resume are more important. Exit 562 from the walled garden may also involve a process to verify that it 563 is indeed the user who is requesting exit from the walled garden and 564 not the bot. 566 Once the user acknowledges the notification, then the user decides to 567 either remediate and then exit the walled garden, or exit the walled 568 garden without addressing the issue. Another approach may be to 569 enforce a stricter policy and require the user to clean the computer 570 prior to permitting the user to exit the walled garden, though this 571 may not be technically feasible depending upon the type of bot, 572 obfuscation techniques employed by a bot, and/or a range of other 573 factors. Thus, the ISP may also need to support tools to scan the 574 infected computer and determine whether it is still infected or rely 575 on user judgment that the bot has been disabled or removed. One 576 challenge with this approach is that if the user has multiple 577 computers sharing a single IP address, such as via a common home 578 gateway device which performs Network Address Translation (NAT). In 579 such a case, the ISP may need to determine from user feedback, or 580 other means, that all affected computers have been remediated, which 581 may or may not be technically feasible. 583 Finally, when a walled garden is used, a list of well-known addresses 584 for both operating system vendors and security vendors should be 585 created and maintained in a white list which permits access to these 586 sites. This can be important for allowing access from the walled 587 garden by end users in search of operating system and application 588 patches. 590 6.5. Instant Message Notification 592 Instant messaging provides the ISP with a simple means to communicate 593 with the user. There are several advantages to using IM which makes 594 it an attractive option. If the ISP provides IM service and the user 595 subscribes to it, then the user can be notified easily. IM-based 596 notification can be a cost effective means to communicate with users 597 automatically from an IM alert system or via a manual process, by the 598 ISP's support staff. Ideally, the ISP should allow the user to 599 register their IM identity in an ISP account management system and 600 grant permission to be contacted via this means. If the IM service 601 provider supports off-line messaging, then the user can be notified 602 regardless of whether they are currently logged into the IM system. 604 There are several drawbacks with this communications method. There 605 is a high probability that subscriber may interpret the communication 606 to be spam, and as such ignore it. Also, not every user uses IM 607 and/or the user may not provide their IM identity to the ISP so some 608 alternative means have to be used. Even in those cases where a user 609 does have an IM address, they may not be signed onto that IM system 610 when the notification is attempted. There maybe also be a privacy 611 concern on the part of users, when such an IM notification must be 612 transmitted over a third-party network and/or IM service. As such, 613 should this method be used, the notification should be discreet and 614 not include any PII in the notification itself. 616 6.6. Short Message Service (SMS) Notification 618 SMS allows the ISP send a brief description of the problem to notify 619 the user of the issue, typically to a mobile device such as a mobile 620 phone or smart phone. Ideally, the ISP should allow the user to 621 register their mobile number and/or SMS address in an ISP account 622 management system and grant permission to be contacted via this 623 means. The primary advantage of SMS is that users are familiar with 624 receiving text messages and are likely to read them. However, users 625 may not act on the notification immediately if they are not in front 626 of their computer system at the time of the SMS notification. 628 One disadvantage is that ISPs may have to follow up with an alternate 629 means of notification if not all of the necessary information maybe 630 conveyed in one message, given constraints on the number of 631 characters in an individual message (typically 140 characters). 632 Another disadvantage with SMS is the cost associated with it. The 633 ISP has to either build its own SMS gateway to interface with the 634 various wireless network service providers or use a third-party SMS 635 clearinghouse (relay) to notify users. In both cases, an ISP will 636 typically pay on a per-message basis to send SMS notifications. An 637 additional downside is that SMS messages sent to a user may result in 638 a charge to the user by their wireless provider, depending upon the 639 plat to which they subscribe. Another minor disadvantage is that it 640 is possible to notify the wrong user if the intended user changes 641 their mobile number but forgets to update it with the ISP. 643 There are several other drawbacks with this communications method. 644 There is a high probability that subscriber may interpret the 645 communication to be spam, and as such ignore it. Also, not every 646 user uses SMS and/or the user may not provide their SMS address or 647 mobile number to the ISP. Even in those cases where a user does have 648 an SMS address or mobile number, their device may not be powered on 649 or otherwise available on a wireless network when the notification is 650 attempted. There maybe also be a privacy concern on the part of 651 users, when such an SMS notification must be transmitted over a 652 third-party network and/or SMS clearinghouse. As such, should this 653 method be used, the notification should be discreet and not include 654 any PII in the notification itself. 656 6.7. Web Browser Notification 658 Near real-time notification to the user's web browser is another 659 technique that may be utilized for notifying the user, though how 660 such a system might operate is outside the scope of this document. 661 Such a notification could have a comparative advantage over a walled 662 garden notification, in that it does not restrict traffic to a 663 specified list of destinations in the same way that a walled garden 664 by definition would. However, as with a walled garden notification, 665 there is no guarantee that a user is at any given time making use of 666 a web browser, though such a system could certainly provide a 667 notification when such a browser is eventually used. Compared to a 668 walled garden, a web browser notification is probably preferred from 669 the perspective of Internet users, as it does not have the risk of 670 disrupting non-web sessions, such as online games, VoIP calls, etc. 671 (as noted in Section 6.4). 673 7. Remediation of Compters Infected with a Bot 675 This section covers the different options available to remediate a 676 computer, which means to remove, disable, or otherwise render a bot 677 harmless. Prior to this step, an ISP has detected the bot, notified 678 the user that one of their computers is infected with a bot, and now 679 may provide some recommended means to clean the computer. The 680 generally recommended approach is to provide the necessary tools and 681 education to the user so that they may perform bot remediation 682 themselves, particularly given the risks and difficulties inherent in 683 attempting to remove a bot. 685 For example, this may include the creation of a special web site with 686 security-oriented content that is dedicated for this purpose. This 687 should be a well-publicized security web site to which a user with a 688 bot infection can be directed to for remediation. This security web 689 site should clearly explain why the user was notified and may include 690 an explanation of what bots are, and the threats that they pose. 691 There should be a clear explanation of the steps that the user should 692 take in order to attempt to clean their computer and provide 693 information on how users can keep the computer free of future 694 infections. The security web site should also have a guided process 695 that takes non-technical users through the remediation process, on an 696 easily understood, step-by-step basis. 698 In terms of the text used to explain what bots are and the threats 699 that they pose, something simple such as this may suffice: 701 "What is a bot? A bot is a piece of software, generally 702 installed on your machine without your knowledge, which either 703 sends spam or tries to steal your personal information. They 704 can be very difficult to spot, though you may have noticed that 705 your computer is running much more slowly than usual or you 706 notice regular disk activity even when you are not doing 707 anything. Ignoring this problem is not really an option since 708 your personal information is currently at risk. Thus, bots 709 need to be removed to protect your data and your personal 710 information." 712 It is also important to note that it may not be immediately apparent 713 to the Internet user precisely which devices have been infected with 714 a particular bot. This may be due to the user's home network 715 configuration, which may encompass several computers, where a home 716 gateway which performs Network Address Translation (NAT) to share a 717 single public IP address has been used. Therefore, any of these 718 devices can be infected with a bot. The consequence of this for an 719 ISP is that remediation advice may not ultimately be immediately 720 actionable by the Internet user, as that user may need to perform 721 additional investigation within their own home network. 723 An added complication is that the user may have a bot infection on a 724 device such as a video console, multimedia system, appliance, or 725 other end-user computing device which does not have a typical Windows 726 or Macintosh user interface. As a result, diligence needs to be 727 taken by the ISP where possible such that they can identify and 728 communicate the specific nature of the device that has been infected 729 with a bot, and further providing appropriate remediation advice. 731 There are a number of forums that exist online to provide security 732 related support to end users. These forums are staffed by volunteers 733 and often are focussed around the use of a common tool set to help 734 end users to remediate computers infected with malware. It may be 735 advantageous to ISPs to foster a relationship with one or more 736 forums, perhaps by offering free hosting or other forms of 737 sponsorship. 739 8. Guided Remediation Process 741 Minimally the Guided Remediation Process should include options 742 and/or recommendations on how a user should: 744 1. Backup personal Documents, for example: "Before you start, make 745 sure to back up all of your important data. (You should do this 746 on a regular basis anyway.) You can back up your files manually 747 or using a system back-up software utility, which may be part of 748 your Operating System (OS). You can back your files up to a USB 749 Thumb Drive (aka USB Key), a CD/DVD-ROM, an external hard drive, 750 or a network file server." 752 2. Download OS patches and Anti-Virus (A/V) software updates. For 753 example, links could be provided to Microsoft Windows updates at 754 http://update.microsoft.com/microsoftupdate/v6/ 755 default.aspx?ln=en-us as well as to Apple MacOS updates at 756 http://support.apple.com/kb/HT1338?viewlocale=en_US. 758 3. Explain how to configure the computer to automatically install 759 updates for the OS, A/V and other common Web Browsers such as 760 Microsoft Internet Explorer, Mozilla Firefox, Apple Safari, 761 Opera, and Google Chrome. 763 4. The flow should also have the option for users to get 764 professional assistance if they are unable to remove the bots 765 themselves. If purchasing third party assistance, then the user 766 should be encouraged to pre-determine how much they are willing 767 to pay for that help. If the computer that is being remediated 768 is old and can easily be replaced with a new, faster, larger and 769 more reliable system for three or four hundred dollars, the it 770 makes no sense to spend five or six hundred dollars to fix the 771 old computer, for example. On the other hand, if the customer 772 has a brand new computer that cost several thousand dollars, it 773 might make perfect sense to spend the money in attempting to 774 remediate it. 776 5. To continue, regardless of whether the user or a knowledgeable 777 technical assistant is working on remediating the computer, their 778 first task should be to determine which of multiple potentially- 779 infected machines may be the one that needs attention (in the 780 common case of multiple computers in a home network). Sometimes, 781 as in cases where there is only a single directly-attached 782 computer, or the user has been noticing problems with one of 783 their computers, this can be easy. Other times, it may be more 784 difficult. If the user is behind a home gateway/router, then the 785 first task may be to ascertain which of the machines is infected. 786 In some cases the user may have to check all machines to identify 787 the infected one. 789 6. User surveys to solicit feedback on whether the notification and 790 remediation process is effective and what recommended changes 791 could be made in order to improve the ease, understandability, 792 and effectiveness the remediation process. 794 7. If the user is interested in reporting his or her computer's bot 795 infection to an applicable law enforcement authority, then the 796 computer effectively becomes a cyber "crime scene" and should not 797 be mitigated unless or until law enforcement has collected the 798 necessary evidence. For individuals in this situation, the ISP 799 should refer them to local, state, federal, or other relevant 800 computer crime offices. (Note: Some "minor" incidents, even if 801 highly traumatic to the user, may not be sufficiently serious for 802 law enforcement to commit some of their limited resources to an 803 investigation.) 805 9. Security Considerations 807 This document describes in detail the numerous security risks and 808 concerns relating to bot nets. As such, it has been appropriate to 809 include specific information about security in each section above. 810 This document describes the security risks related to malicious bot 811 infections themselves, such as enabling identity theft, theft of 812 authentication credentials, and the use of a computer to unwittingly 813 participate in a DDoS attack, among many other risks. This document 814 also describes at a high level the activities that ISPs should be 815 sensitive to, where the collection or communication of PII may be 816 possible. Finally, the document also describes security risks which 817 may relate to the particular methods of communicating a notification 818 to Internet users. Bot networks and bot infections pose extremely 819 serious security risks and any reader should review this document 820 carefully. 822 10. IANA Considerations 824 There are no IANA considerations in this document. 826 11. Acknowledgements 828 The authors wish to acknowledge the following individuals and 829 organisations for their review and feedback of this document: 831 Jonathan Curtis 833 Jeff Chan 835 Roland Dobbins 837 Eliot Gillum 839 The Messaging Anti-Abuse Working Group (MAAWG) 841 Jose Nazario 843 Gunter Ollmann 845 Joe Stewart 847 Eric Ziegast 849 12. Informative references 851 [RFC1459] Oikarinen, J. and D. Reed, "Internet Relay Chat Protocol", 852 RFC 1459, May 1993. 854 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 855 Requirement Levels", BCP 14, RFC 2119, March 1997. 857 [RFC2142] Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND 858 FUNCTIONS", RFC 2142, May 1997. 860 [RFC3954] Claise, B., "Cisco Systems NetFlow Services Export Version 861 9", RFC 3954, October 2004. 863 Appendix A. Document Change Log 865 [RFC Editor: This section is to be removed before publication] 867 -04 version: 869 o Updated reference to BIOS based malware, added wording on PII and 870 local jurisdictions, added suggestion that industry body produce 871 bot stats, added suggestion that ISPs use volunteer forums 873 -03 version: 875 o all updates from Jason - now ready for wider external review 877 -02 version: 879 o all updates from Jason - still some open issues but we're now at a 880 place where we can solicit more external feedback 882 -01 version: 884 o -01 version published 886 Appendix B. Open Issues 888 [RFC Editor: This section is to be removed before publication] 890 Could use some informational references in Section 3 892 Consider revision of the OS update links, to simplify them. 894 Add some point about notification to large networks may not be useful 895 -- such as coffee shops or hotels with WiFi networks. 897 Authors' Addresses 899 Jason Livingood 900 Comcast Cable Communications 901 One Comcast Center 902 1701 John F. Kennedy Boulevard 903 Philadelphia, PA 19103 904 US 906 Email: jason_livingood@cable.comcast.com 907 URI: http://www.comcast.com 909 Nirmal Mody 910 Comcast Cable Communications 911 One Comcast Center 912 1701 John F. Kennedy Boulevard 913 Philadelphia, PA 19103 914 US 916 Email: nirmal_mody@cable.comcast.com 917 URI: http://www.comcast.com 919 Mike O'Reirdan 920 Comcast Cable Communications 921 One Comcast Center 922 1701 John F. Kennedy Boulevard 923 Philadelphia, PA 19103 924 US 926 Email: michael_oreirdan@cable.comcast.com 927 URI: http://www.comcast.com