RTFA: http://www.links.org/files/openid-advisory.txt

Ben Laurie of Google’s Applied Security team, while working with an external researcher, Dr. Richard Clayton of the Computer Laboratory, Cambridge University, found that various OpenID Providers (OPs) had TLS Server Certificates that used weak keys, as a result of the Debian Predictable Random Number Generator (CVE-2008-0166). In combination with the DNS Cache Poisoning issue (CVE-2008-1447) and the fact that almost all SSL/TLS implementations do not consult CRLs (currently an untracked issue), this means that it is impossible to rely on these OPs.

This is an interesting interaction precipitating from a bunch of little things. None of these vulns is too old, and on their own, they’re pretty easy to fix… but with the network scale of things, those unpatched machines that slip through the cracks can be combined in this really weird way, as is described in this article.

…the primary problem seems to be the CRLs, because there are about 32k known bad certificates that all browsers should know to avoid.