450:
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When an entity intercepts the request and returns status 451, it should include a "Link" HTTP header field whose value is a URI reference identifying itself. The "Link" header field must then have a "rel" parameter whose value is "blocked-by". This is intended to identify the entity implementing the
376:
The RFC is specific that a 451 response does not indicate whether the resource exists but requests for it have been blocked, if the resource has been removed for legal reasons and no longer exists, or even if the resource has never existed, but any discussion of its topic has been legally forbidden
473:
When a publisher refuses to serve content to a user, because the user's country adds regulatory requirements that the publisher refuses to comply with, e.g. websites based outside of the EU may refuse to serve users in the EU because they do not want to comply with the
458:
blocking (an ISP, DNS provider, caching system, etc.), not the legal authority mandating the block. At an IETF hackathon, participants used a web crawler to discover that several implementations misunderstood this header and gave the legal authority instead.
372:
it became common practice for websites located outside the EEA to serve HTTP 451 errors to EEA visitors instead of trying to comply with this new privacy law. For instance, many regional U.S. news sites no longer serve web browsers from the EU.
683:
610:
This request may not be serviced in the Roman
Province of Judea due to the Lex Julia Majestatis, which disallows access to resources hosted on servers deemed to be operated by the People's Front of
470:
When content cannot be shown in the user's country, due to contractual or licensing restrictions with the content owner, for example, a TV program may not be available to users in some countries.
320:
protocol to be displayed when the user requests a resource which cannot be served for legal reasons, such as a web page censored by a government. The number 451 is a reference to
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Examples of situations where an HTTP 451 error code could be displayed include web pages deemed a danger to national security, or web pages deemed to violate copyright, privacy,
774:
911:
1120:
942:
466:
The meaning of "a resource which cannot be served for legal reasons" has been interpreted to extend beyond government censorship:
726:
886:
684:"Attorney General Shapiro, Governor Wolf, State Police Successfully Block Access to 3D Downloadable Guns in Pennsylvania"
397:
blacklist, returning a 404 message or another error message instead of showing a message indicating the site is blocked.
385:(missing) or similar if they are not legally permitted to disclose that the resource has been removed. It is used in the
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If the request is for the blocked content then the proxy server will return a 404 error page to the customer
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775:"More than 1,000 U.S. News sites are still unavailable in Europe, two months after GDPR took effect"
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338:, which is often used for the same purpose. This status code is currently a proposed standard in
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An
American website not served to European users to avoid compliance with the
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A 451 error message being displayed when visiting a website in mainland China
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686:(Press release). Pennsylvania Office of Attorney General. 29 July 2018.
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449:
404:, following earlier informal proposals by Chris Applegate in 2008 and
1038:
838:
653:
150:
943:"The HTTP 451 Error Code for Censorship Is Now an Internet Standard"
522:<https://search.example.net/legal>; rel="blocked-by"
487:
1019:
887:"How the IWF blacklist stops you seeing the Scorpions' album cover"
819:
797:
648:
412:
on
December 18, 2015. It was published as in the Proposed Standard
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382:
335:
325:
208:
203:
198:
193:
188:
699:"Call for Ray Bradbury to be honoured with internet error message"
334:, in which books are outlawed. 451 provides more information than
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734:
434:
793:"Major US news sites are still blocking Europeans due to GDPR"
750:"The tyranny of GDPR popups and the websites failing to adapt"
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64:
44:
475:
429:
programme, as an indication of the effects of sanctions on
69:
36:
898:
TCP Reset is sent back to the customer instead of content.
727:"HTTP error code 451: "Unavailable For Legal Reasons""
1059:
29:website to a client in Pennsylvania, 30 July 2018.
400:The status code was formally proposed in 2013 by
1112:
1107:– An HTTP Status Code to Report Legal Obstacles
346:but is not yet formally a part of HTTP, as of
1029:An HTTP Status Code to Report Legal Obstacles
829:An HTTP Status Code to Report Legal Obstacles
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994:
747:
968:
292:
278:
1037:
909:
903:
837:
1121:Hypertext Transfer Protocol status codes
486:
448:
20:
724:
381:). Some sites have previously returned
1113:
912:"There is no HTTP code for censorship"
884:
310:HTTP 451 Unavailable For Legal Reasons
969:Nottingham, Mark (18 December 2015).
940:
934:
696:
1018:
910:Applegate, Chris (9 December 2008).
818:
423:HTTP 451 was mentioned by the BBC's
941:Byrne, Michael (21 December 2015).
885:Arthur, Charles (8 December 2008).
824:"451 Unavailable For Legal Reasons"
361:, or any other law or court order.
13:
493:General Data Protection Regulation
461:
25:A 451 status code returned by the
14:
1137:
1086:
441:, or other Western web services.
214:451 Unavailable for Legal Reasons
1091:
725:Ducklin, Paul (19 August 2013).
408:in 2012. It was approved by the
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1024:"Identifying Blocking Entities"
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962:
748:Matt Burgess (29 August 2018).
222:Security access control methods
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853:
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767:
741:
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697:Flood, Alison (22 June 2012).
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1:
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591:Unavailable For Legal Reasons
557:Unavailable For Legal Reasons
513:Unavailable For Legal Reasons
312:is a proposed standard error
433:and the inability to access
235:Digest access authentication
7:
642:
230:Basic access authentication
10:
1142:
1001:From Our Own Correspondent
482:
426:From Our Own Correspondent
391:Internet service providers
364:After introduction of the
395:Internet Watch Foundation
498:
444:
266:HTTP parameter pollution
243:Security vulnerabilities
261:HTTP response splitting
496:
454:
256:HTTP request smuggling
30:
1100:at Wikimedia Commons
998:(28 September 2017).
490:
452:
251:HTTP header injection
189:301 Moved Permanently
180:Response status codes
24:
1063:(11 November 2017).
1126:Internet censorship
1065:"RFC Errata Report"
1061:Stéphane Bortzmeyer
306:computer networking
27:Defense Distributed
497:
455:
420:in February 2016.
31:
1096:Media related to
1022:(February 2016).
891:Technology blog,
869:Open Rights Group
822:(February 2016).
779:www.niemanlab.org
664:Technological fix
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922:on 19 April 2021
918:. Archived from
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1032:. sec. 4.
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832:. sec. 3.
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462:Additional uses
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171:X-Forwarded-For
79:Request methods
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1087:External links
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731:Naked Security
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393:utilising the
387:United Kingdom
359:blasphemy laws
331:Fahrenheit 451
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209:404 Not Found
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204:403 Forbidden
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199:303 See Other
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137:Header fields
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1090:
1072:. Retrieved
1068:
1055:
1028:
1014:
1000:
996:Sally Hayden
990:
978:. Retrieved
974:
964:
952:. Retrieved
946:
936:
924:. Retrieved
920:the original
916:qwghlm.co.uk
915:
905:
897:
893:The Guardian
890:
880:
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828:
814:
802:. Retrieved
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757:. Retrieved
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708:. Retrieved
704:The Guardian
702:
692:
678:
525:Content-Type
465:
456:
424:
422:
406:Terence Eden
399:
375:
363:
356:
329:
322:Ray Bradbury
309:
303:
213:
161:HTTP referer
18:
1006:BBC Radio 4
980:20 December
975:mnot’s blog
926:23 December
861:"Cleanfeed"
314:status code
60:Compression
55:Persistence
1115:Categories
1074:3 December
1069:IETF Tools
971:"Why 451?"
670:References
379:injunction
1020:Bray, Tim
1004:(radio).
820:Bray, Tim
759:1 October
654:Gag order
565:></
531:text/html
439:App Store
326:dystopian
194:302 Found
1105:RFC 7725
1098:HTTP 451
865:ORG Wiki
798:Engadget
649:Evil bit
643:See also
549:><
402:Tim Bray
389:by some
383:HTTP 404
336:HTTP 403
324:'s 1953
156:Location
804:27 July
710:22 June
483:Example
368:in the
316:of the
123:CONNECT
88:OPTIONS
954:3 July
735:Sophos
611:Judea.
437:, the
435:Airbnb
416:
350:
342:
328:novel
146:Cookie
113:DELETE
754:WIRED
631:</
622:</
613:</
593:</
562:title
559:</
552:title
445:Usage
431:Sudan
377:(see
128:PATCH
118:TRACE
65:HTTPS
1076:2018
1047:7725
982:2015
956:2020
948:Vice
928:2015
847:7725
806:2023
761:2018
712:2012
637:>
634:html
628:>
625:body
619:>
608:>
602:<
599:>
589:>
583:<
580:>
577:body
574:<
571:>
568:head
555:>
546:head
543:<
540:>
537:html
534:<
516:Link
501:HTTP
476:GDPR
418:7725
410:IETF
366:GDPR
352:9110
344:7725
318:HTTP
151:ETag
103:POST
98:HEAD
70:QUIC
37:HTTP
1044:RFC
1034:doi
844:RFC
834:doi
510:451
507:1.1
414:RFC
370:EEA
348:RFC
340:RFC
304:In
166:DNT
108:PUT
93:GET
1117::
1067:.
1042:.
1026:.
973:.
945:.
914:.
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889:.
871:.
867:.
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842:.
826:.
795:.
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752:.
733:.
729:.
701:.
596:h1
586:h1
354:.
308:,
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1008:.
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930:.
849:.
836::
808:.
781:.
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737:.
714:.
616:p
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528::
519::
504:/
495:.
478:.
293:e
286:t
279:v
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
