Sensitive Cookie with Improper SameSite Attribute

Description

The SameSite attribute controls how cookies are sent for cross-domain requests. This attribute may have three values: 'Lax', 'Strict', or 'None'. If the 'None' value is used, a website may create a cross-domain POST HTTP request to another website, and the browser automatically adds cookies to this request. This may lead to Cross-Site-Request-Forgery (CSRF) attacks if there are no additional protections in place (such as Anti-CSRF tokens).

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

In this example, a cookie is used to store a session ID for a client's interaction with a website. The snippet of code below establishes a new cookie to hold the sessionID.

let sessionId = generateSessionId()
let cookieOptions = { domain: 'example.com' }
response.cookie('sessionid', sessionId, cookieOptions)

Since the sameSite attribute is not specified, the cookie will be sent to the website with each request made by the client. An attacker can potentially perform a CSRF attack by using the following malicious page:

<html>

  <form id=evil action="http://local:3002/setEmail" method="POST">

    <input type="hidden" name="newEmail" value="abc@example.com" />

  </form>

<script>evil.submit()</script>
</html>

When the client visits this malicious web page, it submits a '/setEmail' POST HTTP request to the vulnerable website. Since the browser automatically appends the 'sessionid' cookie to the request, the website automatically performs a 'setEmail' action on behalf of the client.

To mitigate the risk, use the sameSite attribute of the 'sessionid' cookie set to 'Strict'.

let sessionId = generateSessionId()
let cookieOptions = { domain: 'example.com', sameSite: 'Strict' }
response.cookie('sessionid', sessionId, cookieOptions)

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Last updated 1 month ago