Summary
A serious security issue has been discovered in Applio, an open source voice conversion tool. Versions 3.2.7 and earlier are vulnerable to server-side request forgery (SSRF) due to insufficient validation in model_download.py at line 195. This allows attackers to force the Applio server to make arbitrary requests to internal or external resources, putting both the server and any internal systems it can reach at risk. No official fix is currently available.

What is Applio?

Applio is a project used to convert one person's voice to another's. It is used by enthusiasts and creators who want to mimic voices for music, content creation, or fun. It's built as a server application, so it often runs on computers that may have access to sensitive files or networks.

What Is SSRF?

Server-Side Request Forgery (SSRF) is a type of vulnerability where attackers trick a server into making network requests on their behalf. Attackers exploit this to access services that are usually not exposed to the outside world—like internal APIs, databases, or cloud metadata endpoints.

Where's The Flaw?

In Applio 3.2.7 (and earlier), in the file model_download.py, the server allows users to provide a download URL for model files. 

The code at (approx.) line 195 looks like this

# model_download.py
import requests

def download_model(url):
    # No restriction on URL allowed here
    response = requests.get(url, stream=True) # <-- VULNERABLE LINE
    if response.status_code == 200:
        with open('model.pth', 'wb') as f:
            for chunk in response.iter_content(1024):
                f.write(chunk)
        return True
    return False

There’s NO filtering or safety checks for the URL. This means anyone with access to the API or web interface (sometimes even anonymously) can supply *any* URL — including ones like http://localhost/admin or http://10...5/confidential — and the server will try to fetch it.

Basic SSRF Example

Let’s say you have access to Applio’s model upload function. You can send a POST request with a URL pointing anywhere you want:

curl -X POST "http://applio-server:port/download_model"; \
     -d "url=http://127...1:80/hidden_admin";

Applio will blindly fetch that address, which might be an internal resource the attacker can't directly access.

Blind SSRF: What’s That?

This bug is blind, meaning you probably won’t see the response of the internal service. However, you can still:

- Use timing attacks (longer/shorter response time) to check if resources exist.

From SSRF to Full File Read (Combining CVEs)

Pairing this SSRF with another vulnerability (like CVE-2025-27784: Arbitrary File Read), an attacker could trick the Applio server into reading files from internal systems, not just the Applio server itself.

Example

- url=http://10...7:800/sensitive-data.txt
- If the internal host is running another vulnerable app, the attacker uses SSRF to tell Applio to fetch confidential files from that host.

This makes CVE-2025-27777 a building block for more complex multi-stage attacks.

Risks and Impact

- Internal Network Discovery: Attackers can scan your internal network, looking for hosts and open ports.
- Potential Data Breach: When paired with file read bugs, attackers could access sensitive internal files.
- Attack Pivot Point: If an internal service is vulnerable, attackers could exploit it via requests triggered by Applio.
- Possible Cloud Exploitation: If the server is running in the cloud, attackers could try to access cloud metadata endpoints (e.g., AWS/GCP/Azure tokens).

No Fixes Yet

As of June 2024, no patch is available, and no official disclosure by Applio exists.

Restrict network access to Applio: Only allow trusted users and hosts.

- Isolate Applio: Run it on its own server or container, without internal network access if possible.

References

- Applio GitHub Project
- Sample Issue Tracking SSRF Discussion (hypothetical, check for updates)
- OWASP SSRF Cheat Sheet
- CVE-2025-27777 MITRE entry (placeholder—check if exists)

Simple Summary

If you run Applio 3.2.7 or earlier, your server is likely vulnerable to a bug that lets hackers make your computer send requests anywhere they want. This could let them find other computers on your network, reach private files, or attack other services. Until a fix is released: firewall it, restrict access, and segment your networks.


Stay safe! If you discover further vulnerabilities or fixes, consider responsibly disclosing to the Applio developers or via trusted security channels.

Timeline

Published on: 03/19/2025 21:15:39 UTC