What is the Same Origin Policy?

Introduction

Today, New browsers provide many built-in security mechanisms to protect against cyberattacks. The Content-Security-Policy, Cookies Policy, Same Origin Policy are few of them.

These built-in mechanisms can not protect us fully, but they provide an extra layer of security that can make hackers work hard.

Here we are going to discuss a browser feature SOP (Same-origin policy).

Same Origin Policy

Before SOP, we need to understand “What is origin”. In this context, origin denotes the exact location of a specific resource such as script, documents, etc.

Mainly origin consists of three elements, The hostname (test.com), the protocol (HTTP or HTTPS), and the ports (80, 443, 8080).

At the time of SOP checks, the browser compares the origin location with the requested resource location.

EXAMPLE: Let’s compare the origin location of this http://old.test.com/dir/ with tables.

URL	Result	Reason
http://old.test.com/dir2/index.html	Same-origin	Same host, protocol, port (only the path differs)
https://old.test.com/dir2/	Failure	Different protocol
http://old.test.com/dir/other.html	Same-origin	only the path differs
http://old.test.com:81/dir/page.html	Failure	Different Port no.
http://new.test.com/dir/page.html	Failure	Different Hostname

The same-origin policy is an important security feature of any browser, Its main purpose is to restrict cross-origin resource sharing like documents, scripts, or media files from one origin to a different origin.

SOP is applicable for a script, documents, It means resources like CSS, Image, etc. can be accessed across origin via the corresponding HTML tags.

Conclusion

A browser can load and display resources from multiple sites and can embed multiple iframes from different sites. If there is no restriction on the browser, a script can be compromised by a hacker, and the script could expose everything in a user’s browser.

Here, SOP acts as a gatekeeper and restricts read access to a resource loaded from a different origin.

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