CookiePro Knowledgebase

dot pattern banner

Knowledgebase Types of Cookies What is an HttpOnly Cookie?


What is an HttpOnly Cookie?

Last Updated: December 11, 2020

An HttpOnly Cookie is a tag added to a browser cookie that prevents client-side scripts from accessing data. It provides a gate that prevents the specialized cookie from being accessed by anything other than the server.  Using the HttpOnly tag when generating a cookie helps mitigate the risk of client-side scripts accessing the protected cookie, thus making these cookies more secure.

The example below shows the syntax used within the HTTP response header:

Set-Cookie: `=“[; “=“]` `[; expires=“][; domain=“]` `[; path=“][; secure][; HttpOnly]`

If the HttpOnly flag is included in the HTTP response header, the cookie cannot be accessed through the client-side script.  As a result, even if a cross-site scripting (XSS) flaw exists, and a user accidentally accesses a link that exploits the flaw, the browser will not reveal the cookie to the third-party.

Here’s an example – let’s say a browser detects a cookie containing the HttpOnly flag.  If the client-side code attempts to read the cookie, the browser will return an empty string as a result.  This helps prevent malicious (usually cross-site scripting (XSS)) code from sending the data to an attacker’s website.

Scan and Categorize Your Website

CookiePro automatically detects and categorizes cookies and other tracking technologies on your website. Click here to sign up for free, no credit card required!

Onetrust All Rights Reserved