To bypass filters, you need to point the service to a server you control, which then redirects the request back to an internal resource.
On your local machine, navigate to the directory where you will create your malicious file and start a simple Python HTTP server:
Write a custom to automate fetching the PDF and parsing out the text.
If you are developing or securing an application that utilizes PDF conversion tools, consider the following mitigations to avoid SSRF and LFI vulnerabilities: pdfy htb writeup upd
Note: In this specific challenge environment, using simple reverse proxy services like Serveo is recommended to avoid browser warning pages that might break the backend parser's automated rendering.
View or download the generated output file. The target file contents will be printed cleanly inside the PDF screenshot structure.
However, because the PDFy interface only takes a URL rather than raw HTML input, we cannot type an tag directly into the input bar. The target server must query an external URL that we control. 3. The Exploitation Strategy: Redirection Bypass To bypass filters, you need to point the
Result: Obtain a service file containing credentials or an internal URL exposing an admin panel.
: PDFy enforces basic input validation. Entering a direct path like file:///etc/passwd into the web interface or attempting to point directly to http://127.0.0.1 triggers an error or block mechanism.
After executing the pdftex exploit:
We can create a malicious configuration file to escalate privileges. Our plan is to create a symbolic link to the /etc/passwd file and modify it to add a new root user.
wait 5 min
The User Proof Data flag is often not in /etc/passwd , but this confirms LFI via SSRF. View or download the generated output file