MSRC doesn’t fix bugs.
I don’t know the specifics of this case, but I’ve managed bug bounty programs in the past through Bountysource and HackerOne. One thing that occasionally happens is that a report makes its way to the development team before the security team has fully assessed it, in this case MSRC.
At that point, a developer may decide to quietly fix the issue. Sometimes that’s driven by a concern, rational or not, that being associated with a security bug could reflect poorly on them or affect future promotion opportunities. The result is that by the time the security team attempts to reproduce the report, the vulnerability is already gone.
From MSRC’s perspective, all they see is that the provided reproduction steps no longer work. They have no visibility into the internal history of the bug or whether someone already patched it. As a result, the report gets closed as invalid even though the original finding may have been legitimate.
If only there were some kind of system for recording the version history and viewing what changes had been made to the code between releases.
Nonsense. As if there are no versions for their software releases.
This is laziness, security absolutely could verify these steps.
That makes sense but doesn't excuse the behavior. Just because there is poor communication within Microsoft doesn't make it okay to silently patch a vulnerability. Also, looking at the timeline on OP's post from 2023 it seems they patched it and closed the bug on the same day which is a little sus .