Cross-origin and cross-site are two very important concepts in web development that are often used interchangeably, but they have different meanings.
Cross-origin refers to resources that are located on different domains, while cross-site usually refers to resources that are located on the same domain but are served by different scripts.
Before we dive in further, let us understand what is 'origin' and 'site'.
Origin
In a URL, the origin represents the combination of the scheme (such as http or https), the domain name (or hostname), and the port number (if specified) that identifies the web application. For instance, if a URL is https://www.example.com:443/foo, then the origin would be https://www.example.com:443. The origin is critical for enforcing web security policies that prevent cross-site attacks.
Site
The term site in the context of a URL refers to the combination of the scheme, Top Level Domain (TLD), and the part of the domain just before TLD, known as TLD+1; (example.com). For instance, if a URL is https://www.example.com:443/foo, then the "site" for the given URL would be https://example.com.
To learn about all the components of a URL, check here.
'same-origin' and 'cross-origin'
Websites that have the combination of the same scheme, hostname, and port are considered "same-origin". Everything else is considered "cross-origin".
Checking for various scenarios with different Origin B values where
Origin A is https://www.example.com:443
| Origin B | Whether Origin A and B are "same-origin" or "cross-origin" |
https://www.evil.com:443 | cross-origin: different domains |
https://example.com:443 | cross-origin: different subdomains |
https://login.example.com:443 | cross-origin: different subdomains |
http://www.example.com:443 | cross-origin: different schemes |
https://www.example.com:80 | cross-origin: different ports |
https://www.example.com:443 | same-origin: exact match |
https://www.example.com | same-origin: implicit port number (443) matches |
'same-site' and 'cross-site'
Websites that have the same scheme and the same TLD+1 are considered "same-site". Websites that have a different scheme or a different TLD+1 are "cross-site".
Checking for various scenarios with different Origin B values where
Origin A is https://www.example.com:443
| Origin B | Whether Origin A and B are "same-site" or "cross-site" |
https://www.evil.com:443 | cross-site: different domains |
https://login.example.com:443 | same-site: different subdomains don't matter |
http://www.example.com:443 | cross-site: different schemes |
https://www.example.com:80 | same-site: different ports don't matter |
https://www.example.com:443 | same-site: exact match |
https://www.example.com | same-site: ports don't matter |
Cross-Origin requests and Cross-Site requests
A cross-origin request is a request that is made from one origin to another. For example, a request from https://www.google.com to https://www.facebook.com is a cross-origin request.
Cross-origin requests are typically blocked by browsers by default, as they can be used to exploit security vulnerabilities. For example, a malicious script could be used to steal cookies or other sensitive information from a user.
A cross-site request is a request that is made from one origin to another, but the request is made from a script that is served from the first origin. For example, a request from https://www.google.com to https://www.facebook.com, but the request is made from a script that is served from https://www.google.com is a cross-site request.
Cross-site requests, on the other hand, are not typically blocked by browsers, as they are not considered to be as risky. However, there are some cases where cross-site requests can be used to exploit security vulnerabilities.
Mitigating risks
In order to mitigate the risks associated with cross-origin and cross-site requests, developers can use a variety of techniques, such as:
Using CORS (Cross-Origin Resource Sharing) to allow specific origins to access resources from other domains.
Using SameSite cookies to prevent cookies from being sent with cross-site requests.
Using Content Security Policy (CSP) to restrict the types of resources that can be loaded from other domains.
By understanding the risks associated with cross-origin and cross-site requests, developers can take steps to mitigate those risks and protect their users.
Conclusion
It is crucial to grasp the concepts of cross-origin and cross-site, which can be manipulated to exploit security vulnerabilities. To mitigate such risks and safeguard users, developers can employ various tactics like CORS to monitor access to resources from different origins and eliminate cross-site scripting attacks by sanitizing user input. Thus, understanding and effectively managing cross-origin and cross-site concepts, along with the associated risks, can play a vital role in enhancing website security and ensuring a secure user experience.