> 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-referer-validation-depends-on-header-presence.md).
# CSRF with Referer Validation Only When Present
CSRF with Referer Validation Only When Present notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### CSRF Where Referer Validation Depends on Header Being Present
The email change functionality of this lab is vulnerable to a CSRF attack. The server tries to block cross-domain requests by checking the header **Referer**, but there is an unsafe fallback management that accepts the query if the Referer header is missing.
* Recommended Account: `wiener:peter` (use this account to reproduce the scenario from the victim).
The server checks the **Referer** field to find out where the request came from and rejects requests whose Referer is not the site's.
* By sending a POST form from the operating server, the answer returns: **"Invalid referer header"** — the check works when the header is present and incorrect.
```html
```
`"Invalid referer header"`
However, if the request arrives **without** referer header, the server accepts the request (dangerous folding behavior).
#### Operating Method (principle)
1. Host a page on the exploit server that submits a POST form to `/my-account/change-email` with the attacking email.
2. Force the exploit page to **remove** browser Referer header so that validation fails as a blocking (since the server accepts the absence of Referer).
3. A simple way to ask the browser not to send Referer is to add a `` tag to the exploit page before submitting the form.
```html
```
---
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