I was updating some third party RPMs on some old servers and I received an error from yum that ended like this:
up2date_client.up2dateErrors.SSLCertificateVerifyFailedError: The certificate is expired. Please ensure you have the correct certificate and your system time is correct.
The host was no longer set to tie into the RHN. Doing a yum info:
Loaded plugins: rhnplugin, security
My hunch was that the rhnplugin was causing the issue. The solution was to run yum like so:
yum --disableplugin=rhnplugin update