> 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/xss/xss-to-bypass-csrf-defenses.md). # XSS to Bypass CSRF Defenses XSS to Bypass CSRF Defenses notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context. ### Exploiting XSS to Bypass CSRF Defenses This lab contains an XSS vulnerability stored in the blog comment feature. The aim is to exploit this vulnerability to steal the CSRF token from a user who consults the comments and then uses it to change the email address of that account. You can connect with the following credentials: `wiener:peter`. * There is a field on the page to update the email.
* There is a field on the page to update the email. * By intercepting the update request the parameters are observed (example): * `email=test%40jord4n.pro` * `CSRF=bChKCyNxiyBR5opUEioECjC9Trutjqyg`
Strategy:
1. Publish a comment containing a script that, when the page is viewed by the victim, recovers HTML from the account page (`/my-account`) using a synchronous or asynchronous query. 2. Exfil this HTML to a controlled listening server (by encoding in base64 if desired). 3. Recover on the attacking side of the CSRF token and, from a second script executed in the victim context, perform a POST query to `/my-account/change-email` by providing both the new address and the recovered CSRF token — the query will use the victim's session cookie as the script runs in its browser. Exfiling the source code of the account page to a listening server (encoded in Base64): ```javascript ```
Observed result: * On our infrastructure listens to two requests containing HTML encoded in base64.
* After decoding, the HTML contains the account information: user name `administrator`, current email, and token CSRF in a `input` field (e.g. `name="csrfa" value="cmqvVFqntB52GNDWvd7VeQjoiAtHfa8M"` in the example provided).
```html

Your username is: administrator

Your email is: admin@normal-user.net

``` Recovery of the CSRF token from HTML and submission of a change of email (POST): ```javascript ``` --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://hacking-notes.jord4n.pro/web/xss/xss-to-bypass-csrf-defenses.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.