> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/web/csrf/csrf-with-duplicated-token-in-a-double-submit-cookie.md). # CSRF with Duplicated Token in a Double-Submit Cookie CSRF with Duplicated Token in a Double-Submit Cookie notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context. ### CSRF Where Token Is Duplicated in Cookie #### Description The email change functionality of this lab is vulnerable to a CSRF attack. The site tries to use the fragile technique of **"double submission"**: the same CSRF token is present in both a form field and a cookie. This protection is insufficient if an attacker can forge a cross-site query that sends a `CSRF` field containing the same value. #### Objective Hosting an HTML page on your **server** that, when the visitor displays, will automatically submit a POST request to change its email address (resolve the lab). #### Access (credentials) You can connect with: `wiener: peter` #### Important Observations from Testing * The value of the CSRF token in the form and the cookie value are identical.
#### Example of CRLF Injection (in the `search` Address Bar or Parameter)
``` hello%0d%0aSet-Cookie:%20csrfKey=qzAd1Kd7ItFul6Ix3H1S3LSXicK8KCfO ```
* To force the cookie to be sent in a cross-site context, it is useful to set `SameSite=None` on the cookie. ``` hello Set-Cookie: csrfKey=qzAd1Kd7ItFul6Ix3H1S3LSXicK8KCfO; SameSite=none hello%0d%0aSet-Cookie:%20csrfKey%3dqzAd1Kd7ItFul6Ix3H1S3LSXicK8KCfO%3b%20SameSite%3dnone ``` #### Exploit HTML to Deposit on the Exploit Server Here is an example of a page that puts the CSRF token value in the `CSRF` field, defines the targeted email, and then submits the form automatically by taking advantage of the image query (which triggers the attempt to write the cookie via the search): ```html
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