It's quite a sad story, when people working in Microsoft used to be the experts of all experts on Windows, and at the present moment people from outside know Windows better... It seems like the only people left in there are maintainers...
Microsoft last patched the tool by manually patching the binary executable. It seems like they don't have the source code for the tool anymore. There was also a long string of vulnerabilities in the tool, which seems to have stopped being updated at source level somewhere around 2000 based on the copyright in the screenshot.
MS should write an alternative to the tool (and I believe they have done so at some point in modern versions of Office), but removing this piece of abandonware was the right call.
“Equation Editor was a formula editor developed by Design Science that allowed users to construct math and science equations in a WYSIWYG environment, and was included in Microsoft Office and several other commercial applications. It was a simplified version of Design Science's MathType”
> MS should write an alternative to the tool (and I believe they have done so at some point in modern versions of Office)
Indeed, and the first version they did that in cannot be called modern anymore. From that same page:
“Beginning with Office 2007, Equation Editor is no longer the default method of creating equations, and is kept for compatibility with old documents only. Instead, a reengineered equation editor is included”
Going back to the Windows 95/98 era and Windows 2k at work I remember a link or line of text in one of the Equation Editor dialogs where they said you could upgrade to the full MathType.
It is the compatibility with old documents that could be an issue with Microsoft's complete removal of the old Equation Editor. I suppose anyone dealing with legacy documents should be using a vm with Win2000 and Office 2000 really.
If you look at the first binary patch for Equation Editor, it's very well done: https://blog.0patch.com/2017/11/did-microsoft-just-manually-... . The problem was that when they fixed it once, other researchers started fuzzing Equation Editor and found many more bugs. Bringing a C++ program from 2000 up to modern security standards when you don't have the source code isn't really feasible, it would be an endless series of whack-a-mole binary patches. I don't really blame Microsoft for dropping support, especially when there's been a replacement equation editor in Office since 2007.
Microsoft wrote their own replacement and it's better-integrated into Office than the old editor was. Search for "insert equation" in the Office search box. The new one supports both the old editor's style of input and actual LaTeX inputs. Heed the dates on articles talking about it: TFA is from 2018 before they wrote the new editor.
You can then download the image. The only thing I think they should add is the equation string as a comment to the images so you can upload and continue editing without a proprietary file format.