Shortly after applying the SUPEE-9767 patch we started to receive complaints from customers that products could not be added to cart from the product detail page.
We are sometimes able to reproduce the issue, but sometimes not.
We are on a fully patched version of EE 1.14.2.2.
Disabling full page cache resolves the issue.
The issue is caused by the Enterprise Page Cache.
The form key is created at:
app/code/core/Enterprise/PageCache/Model/Processor.php:422 which ultimately calls setcookie().
Then the cookie value is retrieved at:
app/code/core/Enterprise/PageCache/Model/Observer.php:1043 in the same request.
As the headers/cookies have not been sent the value returned is null. This causes the core/session cookie to not update with the value Page Cache has just created which is supposed to happen at:
app/code/core/Enterprise/PageCache/Model/Observer.php:1045.
The patch below will resolve this issue. https://gist.github.com/cmtickle/477aba06d8d6a69148de542bfb56ed45
We fixed a 1.14.3.2 installation by backporting the PageCache module entirely from 1.14.3.3. Be careful that the local pool override doesn't work, so we had to edit the core. I hope Ben Marks won't notice what I just wrote.
