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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Nottingham 3 Internet-Draft October 4, 2018 4 Obsoletes: 5785, 8307 (if approved) 5 Updates: 7230, 6455 (if approved) 6 Intended status: Standards Track 7 Expires: April 7, 2019 9 Well-Known Uniform Resource Identifiers (URIs) 10 draft-nottingham-rfc5785bis-08 12 Abstract 14 This memo defines a path prefix for "well-known locations", "/.well- 15 known/", in selected Uniform Resource Identifier (URI) schemes. 17 Note to Readers 19 _RFC EDITOR: please remove this section before publication_ 21 This draft is a proposed revision of RFC5875. 23 The issues list for this draft can be found at 24 https://github.com/mnot/I-D/labels/rfc5785bis [1]. 26 The most recent (often, unpublished) draft is at 27 https://mnot.github.io/I-D/rfc5785bis/ [2]. 29 Recent changes are listed at https://github.com/mnot/I-D/commits/gh- 30 pages/rfc5785bis [3]. 32 See also the draft's current status in the IETF datatracker, at 33 https://datatracker.ietf.org/doc/draft-nottingham-rfc5785bis/ [4]. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at https://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on April 7, 2019. 51 Copyright Notice 53 Copyright (c) 2018 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (https://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 69 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 70 3. Well-Known URIs . . . . . . . . . . . . . . . . . . . . . . . 3 71 3.1. Registering Well-Known URIs . . . . . . . . . . . . . . . 4 72 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 73 4.1. Interaction with Web Browsing . . . . . . . . . . . . . . 6 74 4.2. Scoping Applications . . . . . . . . . . . . . . . . . . 7 75 4.3. Hidden Capabilities . . . . . . . . . . . . . . . . . . . 7 76 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 77 5.1. The Well-Known URI Registry . . . . . . . . . . . . . . . 8 78 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 79 6.1. Normative References . . . . . . . . . . . . . . . . . . 8 80 6.2. Informative References . . . . . . . . . . . . . . . . . 9 81 6.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 10 82 Appendix A. Frequently Asked Questions . . . . . . . . . . . . . 10 83 Appendix B. Changes from RFC5785 . . . . . . . . . . . . . . . . 11 84 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 86 1. Introduction 88 Some applications on the Web require the discovery of information 89 about an origin [RFC6454] (sometimes called "site-wide metadata") 90 before making a request. For example, the Robots Exclusion Protocol 91 (http://www.robotstxt.org/ [5]) specifies a way for automated 92 processes to obtain permission to access resources; likewise, the 93 Platform for Privacy Preferences [P3P] tells user-agents how to 94 discover privacy policy before interacting with an origin server. 96 While there are several ways to access per-resource metadata (e.g., 97 HTTP headers, WebDAV's PROPFIND [RFC4918]), the perceived overhead 98 (either in terms of client-perceived latency and/or deployment 99 difficulties) associated with them often precludes their use in these 100 scenarios. 102 At the same time, it has become more popular to use HTTP as a 103 substrate for non-Web protocols. Sometimes, such protocols need a 104 way to locate one or more resources on a given host. 106 When this happens, one solution is to designate a "well-known 107 location" for data or services related to the origin overall, so that 108 it can be easily located. However, this approach has the drawback of 109 risking collisions, both with other such designated "well-known 110 locations" and with resources that the origin has created (or wishes 111 to create). Furthermore, defining well-known locations usurp's the 112 origin's control over its own URI space [RFC7320]. 114 To address these uses, this memo defines a path prefix in HTTP(S) 115 URIs for these "well-known locations", "/.well-known/". Future 116 specifications that need to define a resource for such metadata can 117 register their use to avoid collisions and minimise impingement upon 118 origins' URI space. 120 Well-known URIs can also be used with other URI schemes, but only 121 when those schemes' definitions explicitly allow it. 123 2. Notational Conventions 125 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 126 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 127 document are to be interpreted as described in RFC 2119 [RFC2119]. 129 3. Well-Known URIs 131 A well-known URI is a URI [RFC3986] whose path component begins with 132 the characters "/.well-known/", and whose scheme is "http" [RFC7230], 133 "https" [RFC7230], "ws" [RFC6455], "wss" [RFC6455], or another scheme 134 that has explicitly been specified to use well-known URIs. 136 Applications that wish to mint new well-known URIs MUST register 137 them, following the procedures in Section 5.1. 139 For example, if an application registers the name 'example', the 140 corresponding well-known URI on 'http://www.example.com/' would be 141 'http://www.example.com/.well-known/example'. 143 Registered names MUST conform to the segment-nz production in 144 [RFC3986]. This means they cannot contain the "/" character. 146 Registered names for a specific application SHOULD be correspondingly 147 precise; "squatting" on generic terms is not encouraged. For 148 example, if the Example application wants a well-known location for 149 metadata, an appropriate registered name might be "example-metadata" 150 or even "example.com-metadata", not "metadata". 152 At a minimum, a registration will reference a specification that 153 defines the format and associated media type(s) to be obtained by 154 dereferencing the well-known URI, along with the URI scheme(s) that 155 the well-known URI can be used with. If no URI schemes are 156 explicitly specified, "http" and "https" are assumed. 158 Typically, applications will use the default port for the given 159 scheme; if an alternative port is used, it MUST be explicitly 160 specified by the application in question. 162 It MAY also contain additional information, such as the syntax of 163 additional path components, query strings and/or fragment identifiers 164 to be appended to the well-known URI, or protocol-specific details 165 (e.g., HTTP [RFC7231] method handling). 167 Note that this specification defines neither how to determine the 168 hostname to use to find the well-known URI for a particular 169 application, nor the scope of the metadata discovered by 170 dereferencing the well-known URI; both should be defined by the 171 application itself. 173 Also, this specification does not define a format or media-type for 174 the resource located at "/.well-known/" and clients should not expect 175 a resource to exist at that location. 177 Well-known URIs are rooted in the top of the path's hierarchy; they 178 are not well-known by definition in other parts of the path. For 179 example, "/.well-known/example" is a well-known URI, whereas 180 "/foo/.well-known/example" is not. 182 See also Section 4 for Security Considerations regarding well-known 183 locations. 185 3.1. Registering Well-Known URIs 187 The "Well-Known URIs" registry is located at 188 "https://www.iana.org/assignments/well-known-uris/". Registration 189 requests can be made by following the instructions located there or 190 by sending an email to the "wellknown-uri-review@ietf.org" mailing 191 list. 193 Registration requests consist of at least the following information: 195 URI suffix: The name requested for the well-known URI, relative to 196 "/.well-known/"; e.g., "example". 198 Change controller: For Standards-Track RFCs, state "IETF". For 199 others, give the name of the responsible party. Other details 200 (e.g., postal address, e-mail address, home page URI) may also be 201 included. 203 Specification document(s): Reference to the document that specifies 204 the field, preferably including a URI that can be used to retrieve 205 a copy of the document. An indication of the relevant sections 206 may also be included, but is not required. 208 Status: One of "permanent" or "provisional". See guidance below. 210 Related information: Optionally, citations to additional documents 211 containing further relevant information. 213 General requirements for registered relation types are described in 214 Section 3. 216 Standards-defined values have a status of "permanent". Other values 217 can also be registered as permanent, if the Experts find that they 218 are in use, in consultation with the community. Other values should 219 be registered as "provisional". 221 Provisional entries can be removed by the Experts if - in 222 consultation with the community - the Experts find that they are not 223 in use. The Experts can change a provisional entry's status to 224 permanent at any time. 226 Note that well-known URIs can be registered by third parties 227 (including the expert(s)), if the expert(s) determines that an 228 unregistered well-known URI is widely deployed and not likely to be 229 registered in a timely manner otherwise. Such registrations still 230 are subject to the requirements defined, including the need to 231 reference a specification. 233 4. Security Considerations 235 Applications minting new well-known URIs, as well as administrators 236 deploying them, will need to consider several security-related 237 issues, including (but not limited to) exposure of sensitive data, 238 denial-of-service attacks (in addition to normal load issues), server 239 and client authentication, vulnerability to DNS rebinding attacks, 240 and attacks where limited access to a server grants the ability to 241 affect how well-known URIs are served. 243 4.1. Interaction with Web Browsing 245 Applications using well-known URIs for "http" or "https" URLs need to 246 be aware that well-known resources will be accessible to Web 247 browsers, and therefore are able to be manipulated by content 248 obtained from other parts of that origin. If an attacker is able to 249 inject content (e.g., through a Cross-Site Scripting vulnerability), 250 they will be able to make potentially arbitrary requests to the well- 251 known resource. 253 HTTP and HTTPS also use origins as a security boundary for many other 254 mechanisms, including (but not limited to) Cookies [RFC6265], Web 255 Storage [WEBSTORAGE] and many capabilities. 257 Applications defining well-known locations should not assume that 258 they have sole access to these mechanisms, or that they are the only 259 application using the origin. Depending on the nature of the 260 application, mitigations can include: 262 o Encrypting sensitive information 264 o Allowing flexibility in the use of identifiers (e.g., Cookie 265 names) to avoid collisions with other applications 267 o Using the 'HttpOnly' flag on Cookies to assure that cookies are 268 not exposed to browser scripting languages [RFC6265] 270 o Using the 'Path' parameter on Cookies to assure that they are not 271 available to other parts of the origin [RFC6265] 273 o Using X-Content-Type-Options: nosniff [FETCH] to assure that 274 content under attacker control can't be coaxed into a form that is 275 interpreted as active content by a Web browser 277 Other good practices include: 279 o Using an application-specific media type in the Content-Type 280 header, and requiring clients to fail if it is not used 282 o Using Content-Security-Policy [CSP] to constrain the capabilities 283 of active content (such as HTML [HTML5]), thereby mitigating 284 Cross-Site Scripting attacks 286 o Using Referrer-Policy [REFERRER-POLICY] to prevent sensitive data 287 in URLs from being leaked in the Referer request header 289 o Avoiding use of compression on any sensitive information (e.g., 290 authentication tokens, passwords), as the scripting environment 291 offered by Web browsers allows an attacker to repeatedly probe the 292 compression space; if the attacker has access to the path of the 293 communication, they can use this capability to recover that 294 information. 296 4.2. Scoping Applications 298 This memo does not specify the scope of applicability for the 299 information obtained from a well-known URI, and does not specify how 300 to discover a well-known URI for a particular application. 302 Individual applications using this mechanism must define both 303 aspects; if this is not specified, security issues can arise from 304 implementation deviations and confusion about boundaries between 305 applications. 307 Applying metadata discovered in a well-known URI to resources other 308 than those co-located on the same origin risks administrative as well 309 as security issues. For example, allowing 310 "https://example.com/.well-known/example" to apply policy to 311 "https://department.example.com", "https://www.example.com" or even 312 "https://www.example.com:8000" assumes a relationship between hosts 313 where there might be none, giving control to a potential attacker. 315 Likewise, specifying that a well-known URI on a particular hostname 316 is to be used to bootstrap a protocol can cause a large number of 317 undesired requests. For example, if a well-known HTTPS URI is used 318 to find policy about a separate service such as e-mail, it can result 319 in a flood of requests to Web servers, even if they don't implement 320 the well-known URI. Such undesired requests can resemble a denial- 321 of-services attack. 323 4.3. Hidden Capabilities 325 Applications using well-known locations should consider that some 326 server administrators might be unaware of its existence (especially 327 on operating systems that hide directories whose names begin with 328 "."). This means that if an attacker has write access to the .well- 329 known directory, they would be able to control its contents, possibly 330 without the administrator realising it. 332 5. IANA Considerations 334 5.1. The Well-Known URI Registry 336 This specification updates the registration procedures for the "Well- 337 Known URI" registry, first defined in [RFC5785]; see Section 3.1. 339 Well-known URIs are registered on the advice of one or more experts 340 (appointed by the IESG or their delegate), with a Specification 341 Required (using terminology from [RFC8126]). 343 The Experts' primary considerations in evaluating registration 344 requests are: 346 o Conformance to the requirements in Section 3 348 o The availability and stability of the specifying document 350 o The considerations outlined in Section 4 352 IANA will direct any incoming requests regarding the registry to this 353 document and, if defined, the processes established by the expert(s); 354 typically, this will mean referring them to the registry Web page. 356 Upon publication, IANA should: 358 o Replace all references to RFC 5988 in that registry have been 359 replaced with references to this document. 361 o Update the status of all existing registrations to "permanent". 363 6. References 365 6.1. Normative References 367 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 368 Requirement Levels", BCP 14, RFC 2119, 369 DOI 10.17487/RFC2119, March 1997, 370 . 372 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 373 Resource Identifier (URI): Generic Syntax", STD 66, 374 RFC 3986, DOI 10.17487/RFC3986, January 2005, 375 . 377 [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, 378 DOI 10.17487/RFC6454, December 2011, 379 . 381 [RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", 382 RFC 6455, DOI 10.17487/RFC6455, December 2011, 383 . 385 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 386 Protocol (HTTP/1.1): Message Syntax and Routing", 387 RFC 7230, DOI 10.17487/RFC7230, June 2014, 388 . 390 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 391 Writing an IANA Considerations Section in RFCs", BCP 26, 392 RFC 8126, DOI 10.17487/RFC8126, June 2017, 393 . 395 6.2. Informative References 397 [CSP] West, M., "Content Security Policy Level 3", World Wide 398 Web Consortium WD WD-CSP3-20160913, September 2016, 399 . 401 [FETCH] WHATWG, "Fetch - Living Standard", n.d., 402 . 404 [HTML5] WHATWG, "HTML - Living Standard", n.d., 405 . 407 [P3P] Marchiori, M., "The Platform for Privacy Preferences 1.0 408 (P3P1.0) Specification", World Wide Web Consortium 409 Recommendation REC-P3P-20020416, April 2002, 410 . 412 [REFERRER-POLICY] 413 Eisinger, J. and E. Stark, "Referrer Policy", World Wide 414 Web Consortium CR CR-referrer-policy-20170126, January 415 2017, 416 . 418 [RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed 419 Authoring and Versioning (WebDAV)", RFC 4918, 420 DOI 10.17487/RFC4918, June 2007, 421 . 423 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known 424 Uniform Resource Identifiers (URIs)", RFC 5785, 425 DOI 10.17487/RFC5785, April 2010, 426 . 428 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, 429 DOI 10.17487/RFC6265, April 2011, 430 . 432 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 433 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 434 DOI 10.17487/RFC7231, June 2014, 435 . 437 [RFC7320] Nottingham, M., "URI Design and Ownership", BCP 190, 438 RFC 7320, DOI 10.17487/RFC7320, July 2014, 439 . 441 [WEBSTORAGE] 442 Hickson, I., "Web Storage (Second Edition)", World Wide 443 Web Consortium Recommendation REC-webstorage-20160419, 444 April 2016, 445 . 447 6.3. URIs 449 [1] https://github.com/mnot/I-D/labels/rfc5785bis 451 [2] https://mnot.github.io/I-D/rfc5785bis/ 453 [3] https://github.com/mnot/I-D/commits/gh-pages/rfc5785bis 455 [4] https://datatracker.ietf.org/doc/draft-nottingham-rfc5785bis/ 457 [5] http://www.robotstxt.org/ 459 Appendix A. Frequently Asked Questions 461 Aren't well-known locations bad for the Web? They are, but for 462 various reasons - both technical and social - they are sometimes 463 necessary. This memo defines a "sandbox" for them, to reduce the 464 risks of collision and to minimise the impact upon pre-existing 465 URIs on sites. 467 Why /.well-known? It's short, descriptive, and according to search 468 indices, not widely used. 470 What impact does this have on existing mechanisms, such as P3P and 471 robots.txt? 472 None, until they choose to use this mechanism. 474 Why aren't per-directory well-known locations defined? Allowing 475 every URI path segment to have a well-known location (e.g., 476 "/images/.well-known/") would increase the risks of colliding with 477 a pre-existing URI on a site, and generally these solutions are 478 found not to scale well, because they're too "chatty". 480 Appendix B. Changes from RFC5785 482 o Allow non-Web well-known locations 484 o Adjust IANA instructions 486 o Update references 488 o Various other clarifications 490 o Add "ws" and "wss" schemes 492 Author's Address 494 Mark Nottingham 496 Email: mnot@mnot.net 497 URI: https://www.mnot.net/