A regression caused by MDL-77130

Patch coming soon

Reproduce:

1. Imaging you have cat1 and cat2 that are siblings
2. You have course1 that is in cat1
3. You have a cohort and its context is cat2

4. cohort_get_cohort($cohort->id, \context_course::instance($course1->id), true);

1.  Above call result supposed to be false, but it returns cohort info

 
Its not really exploitable by a user via UI. However it is possible to use API in 3rd party plugin for example to get cohort info where it shouldn't be allowed
 
It might be reclassified as security benefit issue.