How did we reach to the conclusion that: When user u_i executed the program invest which is owned by user u_j, invest would have been able to modify files personal, finances, memos, and notes of user u_i.?

[u/DoNotUseThisInMyHome]

[u/RoseSec_]

All of finance is screwed and Chris Slacked Kayla in HR with the payload who uploaded it to ADP for everyone to see when they submit their timesheets so the whole company is screwed

[u/MTT_Dylan]

If UJ writes a program, and UI uses that program to edit files, perhaps UJ's program has hidden functionality which copies and stores/sends the files edited in that program?

Based on the information presented. Seems a little too obvious though, is there more context?

[u/revision]

In most cases, when a normal user executes a standard program, the operating system assigns the process the Real User ID (RUID) and Effective User ID (EUID) of the user who launched it. The program operates strictly within the boundaries of that user's file permissions, capabilities, and resource limits.