Firefox Cross-Origin Request Blocked despite headers

Question

I m trying to make a simple cross-origin request  and Firefox is consistently blocking it with this error       Cross-Origin Request Blocked  The Same Origin Policy disallows reading the remote resource at  url   This can be fixed by moving the resource to the same domain or enabling CORS   url     It works fine in Chrome and Safari    As far as I can tell I ve set all the correct headers on my PHP to allow this to work  Here s what my server is responding with   HTTP 1 1 200 OK Date  Mon  23 Jun 2014 17 15 20 GMT Server  Apache 2 2 22  Debian  X-Powered-By  PHP 5 4 4-14 deb7u8 Access-Control-Allow-Origin    Access-Control-Allow-Methods  GET  POST  OPTIONS Access-Control-Allow-Headers  Content-Type Access-Control-Request-Headers  X-Requested-With  accept  content-type Vary  Accept-Encoding Content-Length  186 Content-Type  text html   I ve tried using Angular  jQuery  and a basic XMLHTTPRequest object  like so   var data    id 1234  var request   new XMLHttpRequest  mozSystem  true   request onload   onSuccess  request open  GET    https   myurl com          data  true  request setRequestHeader  Content-Type    application x-www-form-urlencoded   request send        and it works in every browser except  Firefox  Can anyone help with this

User · Answer

If the aforementioned answers don t help then check whether the backend server is up and running or not as in my case the server crashed and this error turns out to be totally misleading

User · Answer

I found that my problem was that the server I ve sent the cross request to had a certificate that was not trusted    If you want to connect to a cross domain with https  you have to add an exception for this certificate first    You can do this by visiting the blocked link once and addibng the exception

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To debug  check server logs if possible  Firefox returns CORS errors in console for a whole range of reasons   One of the reasons is also uMatrix  and I guess NoScript and similar too  plugin

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Ubuntu Firefox giving CORS failed error when my request took more than 10 seconds to process  Nothing to do with CORS  Problem is with ubuntu firefox configuration  I have updated network notify changed to false which made this fix   Mozilla Bugs Reference  https   bugzilla mozilla org show bug cgi id 1238377 https   bugzilla mozilla org show bug cgi id 1235509

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Turns out this has nothing to do with CORS- it was a problem with the security certificate  Misleading errors   4 hours of headaches

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In my case it was my ADBLOCKER  For some reason it was enabled on my localhost and causing this error in Firefox   Disabling it or uninstalling the plugin should fix this   In your case  it may not be an adblocker but another Firefox plugin  Test it out in incognito first with no plugins to determine if that is the issue and then systematically disable the plugins until you find the culprit

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For posterity  also check server logs to see if the resource being requested is returning a 200   I ran into a similar issue  where all of the proper headers were being returned in the pre-flight ajax request  but the browser reported the actual request was blocked due to bad CORS headers   Turns out  the page being requested was returning a 500 error due to bad code  but only when it was fetched via CORS  The browser  both Chrome and Firefox  mistakenly reported that the Access-Control-Allow-Origin header was missing instead of saying the page returned a 500

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If you don t have a  real  certificate  and thus using a self-signed one   in Firefox you can go to  Options  gt  Privacy  amp  Security  gt   scroll to the bottom  View Certificates  gt  Servers  gt  Add Exception     There  fill in the location  eg  https   www myserver myport

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The files are self explanatory  Make a file  call it anything  In my case jq2 php    lt html gt   lt head gt    lt script src  https   ajax googleapis com ajax libs jquery 1 11 3 jquery min js  gt  lt  script gt   lt script gt         document is made ready so that the program starts when we load this page              document  ready function                it tells that any key activity in the  subcat search  filed will execute the query              subcat search   keyup function                    we assemble the get link for the direction to our engine  gs php                var link1    http   127 0 0 1 jqm gs php needle         subcat search   val                   ajax                   url  link1                     ajax function is called sending the input string to  gs php                   success  function result                          result is stuffed in the label                          search val   html result                                                             lt  script gt   lt  head gt    lt body gt    lt  -- the input field for search string -- gt   lt input type  text  id  subcat search  gt   lt br gt   lt  -- the output field for stuffing the output  -- gt   lt label id  search val  gt  lt  label gt    lt  body gt   lt  html gt    Now we will include an engine  make a file  call it anything you like  In my case it is gs php    head    https   maps googleapis com maps api place textsearch json query      our head  key    your key here     your key  hay     GET  needle      hay   str replace            hay     replacing the     with     to design it as per the google s requirement   kill    head    hay     amp key      key    assembling the string in proper way    print file get contents  kill     I have tried to keep the example as simple as possible  And because it executes the link on every keypress  the quota of your API will be consumed pretty fast   Of course there is no end to things we can do  like putting the data into a table  sending to database and so on

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I came across this question having found requests in Firefox were being blocked with the message      Reason  CORS request did not succeed   After pulling my hair out I found out that a newly installed Firefox extension  Privacy Badger  was blocking the requests   If you come to this question after scratching your head  try checking to see what extensions you have installed to see if any of them are blocking requests   See Reason  CORS request did not succeed on MDN for details

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Just add    lt IfModule mod headers c gt      Header set Access-Control-Allow-Origin      lt  IfModule gt    to the  htaccess file in the root of the website you are trying to connect with

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I ve found solution after 2 days         Important note  when responding to a credentialed request  server must   specify a domain  and cannot use wild carding    https   developer mozilla org en-US docs Web HTTP Access control CORS Requests with credentials

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Try this  it should solve your issue   In your config php  add www pre in your domain com  For example   HTTP define  HTTP SERVER    http   domain name with www     HTTPS define  HTTPS SERVER    http   domain name with www      Add this to your  htaccess file  RewriteCond   REQUEST METHOD  OPTIONS RewriteRule         1  R 200 L

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For me  turns out I was setting Access-Control-Allow-Origin response header to a specific  and the correct  host com but it had to be returned as http   host com instead   What does firefox do  It silently swallows the GET request and returns a status 0 to the XHR  with no warnings output to the javascript console  whereas for other similar failures it would at least say something  Ai ai

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Just a word of warnings  I finally got around the problem with Firefox and CORS   The solution for me was this post  Setting CORS  cross-origin resource sharing  on Apache with correct response headers allowing everything through   Benjamin Horn  However Firefox was behaving really  really strange after setting those headers on the Apache server  in the folder  htaccess    I added a lot of console log  Hi FF  you are here A   etc to see what was going on    At first it looked like it hanged on xhr send    But then I discovered it did not get to the this statement  I placed another console log right before it and did not get there - even though there was nothing between the last console log and the new one  It just stopped between two console log   Reordering lines  deleting  to see if there was any strange character in the file  I found nothing   Restarting Firefox fixed the trouble   Yes  I should file a bug  It is just that it is so strange so don t know how to reproduce it    NOTICE  And  oh  I just did the Header always set parts  not the Rewrite  part

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In my case CORS error was happening only in POST requests with file attachments other than small files  After many wasted hours we found out request was blocked for users who were using Kaspersky Total Control  It s possible that other antivirus or firewall software may cause similar problems  Kaspersky run some security tests for requests  but omits them for websites with SSL EV certificate  so obtaining such certificate should resolve this issue properly  Disabling protection for your domain is a bit tricky  so here are required steps  as for December 2020    Settings - gt  Network Settings - gt  Manage exclusions - gt  Add - gt  your domain - gt  Save The good thing is you can detect such blocked request  The error is empty     it doesn t have status and response  This way you can assume it was blocked by third party software and show some info

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I faced similar problem  and I think is valid to be registered how I fixed it   I have a system built basically over Symfony 3  For self learn and performance  purposes I decided to write few scripts using GoLang  also  an API with public access   My Go API expects Json format params  and also return Json format response   To call those GoApi s I am using  most    ajax   jQuery   The first test was a deception  the  un famous  Cross-Origin Request Blocked  pop up   Then  I tried to set the  Access-Control-Allow-Origin     On apache conf  htaccess  php  javascript and anywhere I could find on google    But  even  same frustrating error      The Solution was simple   I had to make  POST  requests instead  GET     To achieve that I had to adjust both  GoLang and JavaScript to use GET   Once it done  no more Cross-Origin Request Blocked for me      Hope it Helps  PS   I am using apache and Vhost  on  Directory Block I have    Header always set Access-Control-Allow-Origin       Header always set Access-Control-Allow-Methods  POST  GET  OPTIONS  DELETE  PUT    Remember       means that you will accept requests from anyone      Which may be a security lack    In my case it is ok  because it will be an public API   PS2  My Headers   Response headers  Access-Control-Allow-Credentials    true Access-Control-Allow-Headers    Authorization Access-Control-Allow-Methods    GET  POST  PUT Access-Control-Allow-Origin http   localhost Content-Length  164 Content-Type    application json  charset UTF-8 Date    Tue  07 May 2019 20 33 52 GMT   Request headers  469 B    Accept  application json  text javascript       q 0 01 Accept-Encoding gzip  deflate Accept-Language en-US en q 0 5 Connection  keep-alive Content-Length  81 Content-Type    application x-www-form-urlencoded  charset UTF-8 Host    localhost 9003 Origin  http   localhost Referer http   localhost fibootkt MY app dev php MyTest GoAPI User-Agent  Mozilla 5 0  Macintosh  Intel      Gecko 20100101 Firefox 66 0

[javascript] Firefox 'Cross-Origin Request Blocked' despite headers

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