Basically, an attacker can grab 64K of memory from a server. The attack leaves no trace, and can be done multiple times to grab a different random 64K of memory. This means that anything in memory — SSL private keys, user keys, anything — is vulnerable. And you have to assume that it is all compromised. All of it.

“Catastrophic” is the right word. On the scale of 1 to 10, this is an 11.

Half a million sites are vulnerable, including my own. Test your vulnerability here.