Login failure after patches 10888, 10975 and 11086

[laura_mill]

I've installed the above patches one at a time onto Magento 1.9.2.4 and ever since I'm unable to login to both admin and customer accounts sections of the site.
I get the "Invalid Form Key" error. I've cleared cookies, cleared cache, cleared session but still get the error.

I've reverted each patch one at a time and cleared all cookies etc out again but I still get the error.
I'm thinking this might mean that the patches have made a change in the database somewhere but not sure where to look.

I've taken a copy of the database from the broken staging site and run in docker on my local but am able to log in with no issues.

I've looked through log files and can't see anything relevant.

I'm not even sure which patch would have caused the error.

Would anybody have any ideas.

[Mukesh Tiwari]

Hi @laura_mill 

Can you share your site's front end url?

Is there any custom module in your site which is extending Mage_Customer module's files?

[laura_mill]

Hi Murkesh,

We do extend the core Magento customer account controller and adjust a couple of the functions but I couldn't find any changes in the core functions that we need to add to our custom ones.

[Vimal Kumar]

Hi @laura_mill 

Please make sure that you have added form key block in every form.

<?php echo $this->getBlockHtml('formkey'); ?>