Mod note: This question is about why XMLHttpRequest/fetch/etc. on the browser are subject to the Same Access Policy restrictions (you get errors mentioning CORB or CORS) while Postman is not. This question is not about how to fix a "No 'Access-Control-Allow-Origin'..." error. It's about why they happen.
Please stop posting:
CORS configurations for every language/framework under the sun. Instead find your relevant language/framework's question.
3rd party services that allow a request to circumvent CORS
Command line options for turning off CORS for various browsers
I am trying to do authorization using JavaScript by connecting to the RESTful API built-in Flask. However, when I make the request, I get the following error:
XMLHttpRequest cannot load http://myApiUrl/login.
No 'Access-Control-Allow-Origin' header is present on the requested resource.
Origin 'null' is therefore not allowed access.
I know that the API or remote resource must set the header, but why did it work when I made the request via the Chrome extension Postman?
This is the request code:
$.ajax({
type: 'POST',
dataType: 'text',
url: api,
username: 'user',
password: 'pass',
crossDomain: true,
xhrFields: {
withCredentials: true,
},
})
.done(function (data) {
console.log('done');
})
.fail(function (xhr, textStatus, errorThrown) {
alert(xhr.responseText);
alert(textStatus);
});
If I understood it right you are doing an XMLHttpRequest to a different domain than your page is on. So the browser is blocking it as it usually allows a request in the same origin for security reasons. You need to do something different when you want to do a cross-domain request.
When you are using Postman they are not restricted by this policy. Quoted from Cross-Origin XMLHttpRequest:
Regular web pages can use the XMLHttpRequest object to send and receive data from remote servers, but they're limited by the same origin policy. Extensions aren't so limited. An extension can talk to remote servers outside of its origin, as long as it first requests cross-origin permissions.
WARNING: Using Access-Control-Allow-Origin: * can make your API/website vulnerable to cross-site request forgery (CSRF) attacks. Make certain you understand the risks before using this code.
It's very simple to solve if you are using PHP. Just add the following script in the beginning of your PHP page which handles the request:
<?php header('Access-Control-Allow-Origin: *'); ?>
If you are using Node-red you have to allow CORS in the node-red/settings.js file by un-commenting the following lines:
// The following property can be used to configure cross-origin resource sharing
// in the HTTP nodes.
// See https://github.com/troygoode/node-cors#configuration-options for
// details on its contents. The following is a basic permissive set of options:
httpNodeCors: {
origin: "*",
methods: "GET,PUT,POST,DELETE"
},
If you are using Flask same as the question; you have first to install flask-cors
pip install -U flask-cors
Then include the Flask cors package in your application.
from flask_cors import CORS
A simple application will look like:
from flask import Flask
from flask_cors import CORS
app = Flask(__name__)
CORS(app)
#app.route("/")
def helloWorld():
return "Hello, cross-origin-world!"
For more details, you can check the Flask documentation.
Because
$.ajax({type: "POST" - calls OPTIONS
$.post( - calls POST
Both are different. Postman calls "POST" properly, but when we call it, it will be "OPTIONS".
For C# web services - Web API
Please add the following code in your web.config file under the <system.webServer> tag. This will work:
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Origin" value="*" />
</customHeaders>
</httpProtocol>
Please make sure you are not doing any mistake in the Ajax call.
jQuery
$.ajax({
url: 'http://mysite.microsoft.sample.xyz.com/api/mycall',
headers: {
'Content-Type': 'application/x-www-form-urlencoded'
},
type: "POST", /* or type:"GET" or type:"PUT" */
dataType: "json",
data: {
},
success: function (result) {
console.log(result);
},
error: function () {
console.log("error");
}
});
Note: If you are looking for downloading content from a third-party website then this will not help you. You can try the following code, but not JavaScript.
System.Net.WebClient wc = new System.Net.WebClient();
string str = wc.DownloadString("http://mysite.microsoft.sample.xyz.com/api/mycall");
Deep
In the below investigation as API, I use http://example.com instead of http://myApiUrl/login from your question, because this first one working. I assume that your page is on http://my-site.local:8088.
NOTE: The API and your page have different domains!
The reason why you see different results is that Postman:
set header Host=example.com (your API)
NOT set header Origin
Postman actually not use your website url at all (you only type your API address into Postman) - he only send request to API, so he assume that website has same address as API (browser not assume this)
This is similar to browsers' way of sending requests when the site and API has the same domain (browsers also set the header item Referer=http://my-site.local:8088, however I don't see it in Postman). When Origin header is not set, usually servers allow such requests by default.
This is the standard way how Postman sends requests. But a browser sends requests differently when your site and API have different domains, and then CORS occurs and the browser automatically:
sets header Host=example.com (yours as API)
sets header Origin=http://my-site.local:8088 (your site)
(The header Referer has the same value as Origin). And now in Chrome's Console & Networks tab you will see:
When you have Host != Origin this is CORS, and when the server detects such a request, it usually blocks it by default.
Origin=null is set when you open HTML content from a local directory, and it sends a request. The same situation is when you send a request inside an <iframe>, like in the below snippet (but here the Host header is not set at all) - in general, everywhere the HTML specification says opaque origin, you can translate that to Origin=null. More information about this you can find here.
fetch('http://example.com/api', {method: 'POST'});
Look on chrome-console > network tab
If you do not use a simple CORS request, usually the browser automatically also sends an OPTIONS request before sending the main request - more information is here. The snippet below shows it:
fetch('http://example.com/api', {
method: 'POST',
headers: { 'Content-Type': 'application/json'}
});
Look in chrome-console -> network tab to 'api' request.
This is the OPTIONS request (the server does not allow sending a POST request)
You can change the configuration of your server to allow CORS requests.
Here is an example configuration which turns on CORS on nginx (nginx.conf file) - be very careful with setting always/"$http_origin" for nginx and "*" for Apache - this will unblock CORS from any domain (in production instead of stars use your concrete page adres which consume your api)
location ~ ^/index\.php(/|$) {
...
add_header 'Access-Control-Allow-Origin' "$http_origin" always;
add_header 'Access-Control-Allow-Credentials' 'true' always;
if ($request_method = OPTIONS) {
add_header 'Access-Control-Allow-Origin' "$http_origin"; # DO NOT remove THIS LINES (doubled with outside 'if' above)
add_header 'Access-Control-Allow-Credentials' 'true';
add_header 'Access-Control-Max-Age' 1728000; # cache preflight value for 20 days
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
add_header 'Access-Control-Allow-Headers' 'My-First-Header,My-Second-Header,Authorization,Content-Type,Accept,Origin';
add_header 'Content-Length' 0;
add_header 'Content-Type' 'text/plain charset=UTF-8';
return 204;
}
}
Here is an example configuration which turns on CORS on Apache (.htaccess file)
# ------------------------------------------------------------------------------
# | Cross-domain Ajax requests |
# ------------------------------------------------------------------------------
# Enable cross-origin Ajax requests.
# http://code.google.com/p/html5security/wiki/CrossOriginRequestSecurity
# http://enable-cors.org/
# <IfModule mod_headers.c>
# Header set Access-Control-Allow-Origin "*"
# </IfModule>
# Header set Header set Access-Control-Allow-Origin "*"
# Header always set Access-Control-Allow-Credentials "true"
Access-Control-Allow-Origin "http://your-page.com:80"
Header always set Access-Control-Allow-Methods "POST, GET, OPTIONS, DELETE, PUT"
Header always set Access-Control-Allow-Headers "My-First-Header,My-Second-Header,Authorization, content-type, csrf-token"
Applying a CORS restriction is a security feature defined by a server and implemented by a browser.
The browser looks at the CORS policy of the server and respects it.
However, the Postman tool does not bother about the CORS policy of the server.
That is why the CORS error appears in the browser, but not in Postman.
The error you get is due to the CORS standard, which sets some restrictions on how JavaScript can perform ajax requests.
The CORS standard is a client-side standard, implemented in the browser. So it is the browser which prevent the call from completing and generates the error message - not the server.
Postman does not implement the CORS restrictions, which is why you don't see the same error when making the same call from Postman.
Why doesn't Postman implement CORS? CORS defines the restrictions relative to the origin (URL domain) of the page which initiates the request. But in Postman the requests doesn't originate from a page with an URL so CORS does not apply.
Solution & Issue Origins
You are making a XMLHttpRequest to different domains, example:
Domain one: some-domain.com
Domain Two: some-different-domain.com
This difference in domain names triggers CORS (Cross-Origin Resource Sharing) policy called SOP (Same-Origin Policy) that enforces the use of same domains (hence Origin) in Ajax, XMLHttpRequest and other HTTP requests.
Why did it work when I made the request via the Chrome extension
Postman?
A client (most Browsers and Development Tools) has a choice to enforce the Same-Origin Policy.
Most browsers enforce the policy of Same-Origin Policy to prevent issues related to CSRF (Cross-Site Request Forgery) attack.
Postman as a development tool chooses not to enforce SOP while some browsers enforce, this is why you can send requests via Postman that you cannot send with XMLHttpRequest via JS using the browser.
For browser testing purposes:
Windows - Run:
chrome.exe --user-data-dir="C://Chrome dev session" --disable-web-security
The command above will disable chrome web security. So for example if you work on a local project and encounter CORS policy issue when trying to make a request, you can skip this type of error with the above command. Basically it will open a new chrome session.
You might also get this error if your gateway timeout is too short and the resource you are accessing takes longer to process than the timeout. This may be the case for complex database queries etc. Thus, the above error code can be disguishing this problem. Just check if the error code is 504 instead of 404 as in Kamil's answer or something else. If it is 504, then increasing the gateway timeout might fix the problem.
In my case the CORS error could be removed by disabling the same origin policy (CORS) in the Internet Explorer browser, see How to disable same origin policy Internet Explorer. After doing this, it was a pure 504 error in the log.
To resolve this issue, write this line of code in your doGet() or doPost() function whichever you are using in backend
response.setHeader("Access-Control-Allow-Origin", "*");
Instead of "*" you can type in the website or API URL endpoint which is accessing the website else it will be public.
Your IP address is not whitelisted, so you are getting this error.
Ask the backend staff to whitelist your IP address for the service you are accessing.
Access-Control-Allow-Headers
For me I got this issue for different reason, the remote domain was added to origins the deployed app works perfectly except one end point I got this issue:
Origin https://mai-frontend.vercel.app is not allowed by Access-Control-Allow-Origin. Status code: 500
and
Fetch API cannot load https://sciigo.herokuapp.com/recommendations/recommendationsByUser/8f1bb29e-8ce6-4df2-b138-ffe53650dbab due to access control checks.
I discovered that my Heroku database table does not contains all the columns of my local table after updating Heroku database table everything worked well.
It works for me by applying this middleware in globally:
<?php
namespace App\Http\Middleware;
use Closure;
class Cors {
public function handle($request, Closure $next) {
return $next($request)
->header('Access-Control-Allow-Origin', '*')
->header('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS')
->header('Access-Control-Allow-Headers', "Accept,authorization,Authorization, Content-Type");
}
}
I have a grails 2.2.4 application. I wanted to enable CORS
So I installed cors plugin by having the following line in build config.
plugins {
runtime ':cors:1.1.8'
}
Then in the config.groovy
cors.headers = ['Access-Control-Allow-Origin': '*']
But after this when I run the application, CORS in not enabled. So I debugged the CORS plugin. The issue seems to be in CorsFilter class in the following method
private boolean checkOrigin(HttpServletRequest req, HttpServletResponse resp) {
String origin = req.getHeader("Origin");
if (origin == null) {
//no origin; per W3C spec, terminate further processing for both preflight and actual requests
return false;
}
The origin parameter in the above line is always null as the request does not have the parameter 'Origin'. Is there something i'm doing wrong? I'm not looking for the answer which says add a manual header with the name "Origin" since that is not exactly a proper fix
I'm quite new to CORS so appriciate the help.
In addition to Access-Control-Allow-Origin, and in addition to setting the Origin header on request, you probably need to specify these response headers as well:
Access-Control-Allow-Headers: accept
Access-Control-Allow-Headers: origin
Access-Control-Allow-Headers: content-type
Access-Control-Allow-Method: GET
Access-Control-Allow-Method: POST
Also make sure you respond to HTTP OPTIONS requests with these headers and a blank 200 OK response.
For now, let's assume that RestClient is sending the Origin header properly. It may still be getting stripped by your application. You can prevent this using the Access-Control-Allow-Headers: Origin header.
Most of the problems I have had with my web services is that the right headers are being sent, but they are stripped from the message by my web server. So I tend to adopt a shotgun approach of "allow everything" and then one by one remove what I don't need. My allow-headers header usually is pretty long and I end up having to include stuff like Content-Type, X-Requested-With and other junk before my requests will finally go through.
I further recommend that you test using something besides RestClient, if only as a sanity check. I use Postman, a free Chrome app, for all my messaging tests. It looks to me like the problem is with RestClient not sending the proper Origin header.
I am currently trying to write an auxiliary module for Metasploit. The module basically tries multiple default credentials to get access to the router's management page. The authentication is done via web, i.e. HTTP POST.
Currently, the module works as expected for plain HTTP connections, i.e. unsecured connections, however every connection attempt via HTTPS (port 443), returns nil. Below is the function used within the Metasploit class to retrieve the login page:
def get_login_page(ip)
begin
response = send_request_cgi(
'uri' => '/',
'method' => 'GET'
)
# Some models of ZyXEL ZyWALL return a 200 OK response
# and use javascript to redirect to the rpAuth.html page.
if response && response.body =~ /changeURL\('rpAuth.html'\)/
vprint_status "#{ip}- Redirecting to rpAuth.html page..."
response = send_request_cgi(
'uri' => '/rpAuth.html',
'method' => 'GET'
)
end
rescue ::Rex::ConnectionError
vprint_error "#{ip} - Failed to connect to Web management console."
end
return response
end
When trying to connect via HTTPS, the first send_request_cgi call returns nil. No exception are caught or thrown. I have tried with 3 different hosts to make sure the issue was not with a specific endpoint. All my 3 attempts failed to return a response. At every attempt, I set the RPORT option to 443;
RHOSTS 0.0.0.0 yes The target address range or CIDR identifier
RPORT 443 yes The target port
Note that I have replaced the real IP with 0.0.0.0. Using a web browser, I can actually connect to the router via HTTPS with no issue (other than having to add an exception since the certificate is untrusted) and am presented the login page. With Wireshark, I tried to look at the generated traffic. I can clearly see that nothing is sent by the router. I notice the 3-way handshake being completed and the HTTP GET request being made:
GET / HTTP/1.1
Host: 0.0.0.0
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
Content-Type: application/x-www-form-urlencoded
Content-Length: 0
There are 3-4 ACK after and then a FIN/PUSH sent by the server.
Based on this page on Metasploit's GitHub, I was under the impression that connections to HTTPS websites were handled by the underlying framework. I have not seen any articles/tutorial/source that leads me to believe otherwise. The doc about the send_request_cgi does not specify any specific requirement to establish a HTTPS connection. Other posts did not had the exact same issue I'm having. At this point I suspect either the OS, the framework or me forgetting to enable something. Other modules I have looked at either only targets HTTP websites - which I doubt - or do not have any special handling for HTTPS connections.
Any help determining the cause would be greatly appreciated.
Version of Metasploit:
Framework: 4.9.3-2014060501
Console : 4.9.3-2014060501.15168
Version of OS:
SMP Debian 3.14.5-1kali1 (2014-06-07)
As per this post on SecurityStreet, the solution was to set SSL to true in the DefaultOptions in the initialize function:
def initialize
super(
...
'DefaultOptions' =>
{
...
'SSL' => true
}
)
...
end
Connections to routers using HTTPS worked afterwards.
I put code from end of this article to my MVC controller method:
http://msdn.microsoft.com/en-us/library/windowsazure/gg680299.aspx
I configured cname for cdn and all working fine except I feel that cdn not caching :)
There is CDN url
http://cdn.services.idemkvrachu.ru/services/BranchLogo/82f204fe-bb1d-4204-b817-d424e1284b17/E0F4F2AE-B6C2-4516-BE7C-59B649E2C5AC?lastUpdated=635169430040919922&width=499
And this is original url
http://prm.idemkvrachu.ru/cdn/services/BranchLogo/82f204fe-bb1d-4204-b817-d424e1284b17/E0F4F2AE-B6C2-4516-BE7C-59B649E2C5AC?lastUpdated=635169430040919922&width=499
This is my code:
Response.Cache.SetExpires(DateTime.Now.AddDays(14));
Response.Cache.SetCacheability(HttpCacheability.Public);
Response.Cache.SetLastModified(blob.ChangDateOfs.DateTime);
return File(bytes, format);
When I checked timings receiving picture from original link and cdn - I found that timings higher on cdn.
Also I was trying change blob.ChangDateOfs and comparing Last-Modified header from cdn response: it immediately changes.
What's wrong with my code? Maybe this header breaks cdn cache Cache-Control public, no-cache="Set-Cookie" ?
To troubleshoot caching issues the first thing you want to do is validate if your content is actually getting cached or not.o
To do this you can add the X-LDebug header with a value of 2. An example of doing this against your endpoint with the relevant portions of output included:
C:\Azure\Tools\wget\bin>wget -S --header "X-LDebug:2" http://cdn.services.idemkvrachu.ru/services/BranchLogo/82f204fe-bb1d-4204-b817-d424e1284b17/E0F4F2AE-B6C2-4516-BE7C-59B649E2C5AC?lastUpdated=635169430040919922&width=499
Cache-Control: public, no-cache="Set-Cookie"
Set-Cookie: ASP.NET_SessionId=nnxb3xqdqetj0uhlffdmtf03; path=/; HttpOnly
Set-Cookie: idCity=31ed5892-d3cb-45eb-bd4f-526cd65f5302; domain=idemkvrachu.cloudapp.net;
X-Cache: MISS from cds173.sat9.msecn.net
As you can see, you are setting the Cache-Control header to no-cache="Set-Cookie", and then are setting a cookie. This is telling the CDN to not cache the content. Since your code is only setting the cache control to Public I assume that you have a setting in your web.config or aspx page that is modifying the cache control header to add the no-cache="Set-Cookie".