400 Bad Request on account or admin login On attempting to login into either a front-end account or admin account I'm hit by:

400 Bad Request
Request Header Or Cookie Too Large
nginx/1.8.0

It's only happened recently but running the latest Craft CMS v2.5.2757 and from looking at the cookies created during login I think it's possibly related to CSRF protection as deleting the top cookie in the list below fixes the issue until you log in again.



Running a few other Craft sites on the same staging nGinx server without the same issue, and even the same codebase is running another site without issue.

Any thoughts please?!
Add this to your nginx server block:

server {
  ...
  large_client_header_buffers 4 16k;
  ...
} 


and restart nginx. The default is 8k. If you have a lot of headers, beefing that value up should resolve it otherwise you may want to play with client_header_buffer_size as well.