Modernize and secure temp file creation

[pixeebot]

This change replaces the usage of java.io.File#createTempFile with java.nio.file.Files#createTempFile which has more secure attributes.

The java.io.File#createTempFile() method creates a file that is world-readable and world-writeable, which is almost never necessary. Also, the file created is placed in a predictable directory (e.g., /tmp). Having predictable file names, locations, and will lead to many types of vulnerabilities. History has shown that this insecure pattern can lead to information leakage, privilege escalation and even code execution.

Our changes look something like this:

+  import java.nio.file.Files;
   ...
-  File txtFile = File.createTempFile("acme", ".txt");
+  File txtFile = Files.createTempFile("acme", ".txt").toFile();

More reading

• https://cwe.mitre.org/data/definitions/378.html
• https://docs.fluidattacks.com/criteria/vulnerabilities/160/
• create temporary file in directory with secure permissions  apache/druid#11130
• https://owasp.org/www-community/vulnerabilities/Insecure_Temporary_File
• https://nvd.nist.gov/vuln/detail/CVE-2022-41954
• https://www.cvedetails.com/vulnerability-list/cwe-378/vulnerabilities.html

I have additional improvements ready for this repo! If you want to see them, leave the comment:

@pixeebot next

... and I will open a new PR right away!

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[pixeebot]

I'm confident in this change, but I'm not a maintainer of this project. Do you see any reason not to merge it?

If this change was not helpful, or you have suggestions for improvements, please let me know!

[hmsloaner]

@pixeebot next

[pixeebot]

@hmsloaner, I opened PR #4, go check it out!