Fix Sensitive Data Exposure: Set `umask` to default value after use

What kind of change does this PR introduce?

[x] bug fix
[ ] feature
[ ] docs update
[ ] tests/coverage improvement
[ ] refactoring
[ ] other

Other information:

Details

While triaging your project, our bug fixing tool generated the following message(s)-

In file: plugins.py, there is a method daemonize that grants permission to the others class which refers to all users except the owner and member of the file's group class. This may lead to undesired access to a confidential file. iCR replaced the loose permission with a stricter permission.

Notes

According to your codebase and comments, it seems that the os.umask(0) has to be called in order to daemonize a process. However, it's suggested that the umask value be set to default after the daemonizing task. Otherwise the umask value could propagate for the rest of the codebase and may introduce vulnerability.

Proof of Concept

POC - Sensitive Data Exposure - umask - CherryPy.mp4

Example Source Code:

import os.path
import cherrypy
from cherrypy.process.plugins import Daemonizer

class HelloWorld:
    """ Sample request handler class. """
    # ...
    @cherrypy.expose
    def index(self):
        # ...
        with open("test_daemonize_webserver", "w") as f:
            f.write("I'm writing this from the webserver")
        mask = os.umask(0o644)
        return 'Hello world!'

with open("test_daemonize_before", "w") as f:
    f.write("I'm writing this before daemonizing")

# Let's daemonize the process
Daemonizer(cherrypy.engine).subscribe()
tutconf = os.path.join(os.path.dirname(__file__), 'tutorial.conf')

if __name__ == '__main__':
    # ...
    cherrypy.quickstart(HelloWorld(), config=tutconf)

Changes

Set the os.umask value to what it was before after daemonizing the process. For example -

Previously Found & Fixed

https://github.com/django-helpdesk/django-helpdesk/pull/1120

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Sponsorship and Support

This work is done by the security researchers from OpenRefactory and is supported by the Open Source Security Foundation (OpenSSF): Project Alpha-Omega. Alpha-Omega is a project partnering with open source software project maintainers to systematically find new, as-yet-undiscovered vulnerabilities in open source code - and get them fixed – to improve global software supply chain security.

The bug is found by running the Intelligent Code Repair (iCR) tool by OpenRefactory and then manually triaging the results.

Checklist:

[x] I think the code is well written
[x] I wrote good commit messages
[ ] I have squashed related commits together after the changes have been approved
[ ] Unit tests for the changes exist
[ ] Integration tests for the changes exist (if applicable)
[x] I used the same coding conventions as the rest of the project
[x] The new code doesn't generate linter offenses
[ ] Documentation reflects the changes
[x] The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences

cherrypy / cherrypy