What are the security implications of this fix for the "unsandboxed" apt notes?
An article at https://devicetests.com/fix-download-unsandboxed-root-error-ubuntu presents a fix for the inconsequential yet annoying "unsandboxed download" notes produced by apt.
Reference: What does this apt error message ("Download is performed unsandboxed as root…") mean? (I learned about this fix in a downvoted and soon-to-be-deleted answer to this question)
The solution presented is to create the file /etc/apt/apt.conf.d/10sandbox with contents APT::Sandbox::User "root";
Testing the solution in a 20.04 VM shows that it works insofar as the messages are not emitted.
However, the article warns ominously that there may be "security implications" by using this method, but provides no further info.
What are the "security implications" of using this method?
The security implications of the download running as root is that if someone is manipulating your network traffic and there is a security vulnerability in apt, the attacker might be able to exploit that vulnerability and take over your computer.
This is not an immediate danger, but still, it’s not a good idea to just hide that message. The article you linked is no fix to the underlying issue, it just hides that message.
Please find out why you might be getting that message and fix it (the linked question gives some details).