My site (4.5.3 on Apache/Linux) was hacked, I suspect something like the one described here. As best I can tell I've removed or at least disabled the hack, however admin users aren't able to perform actions like updating WordPress, adding plugins, etc.
So far, I have tried:
- Editing the existing admin user's permissions via phpMyAdmin.
- Adding a completely new admin user via phpMyAdmin.
- Overwriting core WP files with those from a fresh download (of the same version currently installed).
- Disabled (and then completely removed) all plugins.
All to no avail. Any thoughts on what I can try next?