Description

pyLoad allows upload to arbitrary folder lead to RCE

Summary

An authenticated user can change the download folder and upload a crafted template to the specified folder lead to remote code execution

Details

example version: 0.5 file:src/pyload/webui/app/blueprints/app_blueprint.py

@bp.route("/render/<path:filename>", endpoint="render")
def render(filename):
    mimetype = mimetypes.guess_type(filename)[0] or "text/html"
    data = render_template(filename)
    return flask.Response(data, mimetype=mimetype)

So, if we can control file in the path "pyload/webui/app/templates" in latest version and path in "module/web/media/js"(the difference is the older version0.4.20 only renders file with extension name ".js"), the render_template func will works like SSTI(server-side template injection) when render the evil file we control.

in /settings page and the choose option general/general, where we can change the download folder.

Also, we can find the pyLoad install folder in /info page So, we can change the value of Download folder to the template path. Then through /json/add_package we can upload a crafted template file to RCE.

@bp.route("/json/add_package", methods=["POST"], endpoint="add_package")
# @apiver_check
@login_required("ADD")
def add_package():
    api = flask.current_app.config["PYLOAD_API"]

    package_name = flask.request.form.get("add_name", "New Package").strip()
    queue = int(flask.request.form["add_dest"])...
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PoC

First login into the admin page, then visit the info page to get the path of pyload installation folder. Second, change the download folder to PYLOAD_INSTALL_DIR/ webui/app/templates/ Third, upload crafted template file through /json/add_package through parameter add_file the content of crafted template file and its filename is "341.html":

{{x.__init__.__globals__['__builtins__']['eval']("__import__('os').popen('whoami').read()")}}

Last, visit http://TARGET/render/tmp_341.html to trigger the RCE

Impact

It is a RCE vulnerability and I think it affects all versions. In earlier version 0.4.20, the trigger difference is the pyload installation folder path difference and the upload file must with extension ".js" . The render js code in version 0.4.20:

@route("/media/js/<path:re:.+\.js>")
def js_dynamic(path):
    response.headers['Expires'] = time.strftime("%a, %d %b %Y %H:%M:%S GMT",
                                                time.gmtime(time.time() + 60 * 60 * 24 * 2))
    response.headers['Cache-control'] = "public"
    response.headers['Content-Type'] = "text/javascript; charset=UTF-8"

    try:...
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Mitigation

Aliases

References