![]() Resource using OPTIONS method, in which he queries access to the resource PUT, DELETE) that are not allowed by SOP,ĬORS-enabled browser first send preflight request to the To request resources with custom headers or using custom HTTP methods Of CORS will not expose any additional information, except allowed by the (optionally allowing exposing custom server headers to the page andĮnabling use of the user credentials on the server resource): Access-Control-Allow-Origin: Īccess-Control-Expose-Headers: X-Server-Headerīrowser checks, if server responded with properĪccess-Control-Allow-Origin header and accordingly allows or deniesĪccess for the obtained resource to the page.ĬORS specification designed in a way that servers that are not aware Resource with Access-Control-Allow-Origin: If server allows access from the page to the resource, it responds with The resource to the page: GET /resource HTTP/1.1 In short, CORS works in the following way.īrowser implicitly appends Origin: headerĮffectively requesting server to give read permission for Cross-origin resource sharingĬross-origin Resource Sharing (CORS) allows to override Screenshot of the embedded internet banking page). (which may be not only source code, but, for example, Then read user private information by reading source of the embedded page User is directly navigated to internet banking page), (since authentication is done by the browser it may be embedded as if Malicious page would be able to embed internet banking page with iframe cookies, HTTP Basic Authentication).įor example, if Read would be allowed and user is authenticated When browser reads (downloads) resource he automatically sends all securityĬredentials that user previously authorized for that resource ![]() Restriction to Read resource from other origin is related to authentication Other origin with limited set of Content-Type values and headers. ![]() Limited ability to Write means, that the page can send POST requests to the page can read embedded image dimensions). (though some information from the other resource may still be leaked:Į.g. ( source - any information that would allow to reconstruct resource).īut it can’t get information about specific pixels, so page can’t reconstruct (there is a notable exception with Internet Explorer: it doesn’t use port toĬan Embed means that resource from other origin can be embedded intoĬannot Read means that resource from other origin source cannot be Origin of a page is defined in the Standard as tuple Resources and have limited ability to Write resources. In short: web pages cannot Read resources which originĭoesn’t match origin of requested page, but can Embed (or Execute) ![]() Web security model is tightly connected to Jump directly to Usage part to see how to use aiohttp_cors. Asyncio-powered asynchronous HTTP server. ![]()
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