What would you do if someone from your alma mater reaches out to you for your company review?

Some facts I've realised are -

1. Your alumni will be the closest thing to your friends/family you'll find in this highly competitive world. More so, if you graduated from a reputed college.
2. To get that trust, you need to give something in return. Be kind and support your alumni wherever needed coz you'll never know when you would them in future jobs.
3. Do not be selfish/foolish to deceive your alumni. No one will bother to refer you in a highly sought after job, unless you have a alumni referral there.
4. Some people have mentioned in comments, try Glassdoor. That works, but I believe being open and showing that you personally spoke to deliver the truth speaks volumes over sending them to some loophole in Glassdoor

Ask them to check glass door and wash your hands off.

Write an honest review on Glassdoor. Then, let them know they should definitely check the latest reviews on Glassdoor.

I've been through this. I usually tell them the pros and cons over a call and add the caveat that the work-culture is limited to the teams they're going to be part of, and that each team has its own way of functioning. They'll quite understand.

If your organisation on the whole is in deep shit, then maybe talk about the macro factors affecting it (you're giving them subtle hints to not join), instead of directly bitching about the org. If they're smart enough they will get it, and the ones desperate for a job/tag will still go ahead. You can only do so much.

Basically, beat around the bush with a lot of caveats. :)

Don't get your hands dirty. You'll face action. Also if the company is trying to change things and you're not in the loop maybe you're telling the candidates something that might not been true anymore.