We have published a technical report, Imperfect Forward Secrecy: How Diffie-Hellman Fails in Practice, which has specifics on these attacks, details on how we broke the most common 512-bit Diffie-Hellman group, and measurements of who is affected. We have also published several proof of concept demos and a Guide to Deploying Diffie-Hellman for TLS.

Source: Logjam: How Diffie-Hellman Fails in Practice

What should I do?

If you run a server…

If you have a web or mail server, you should disable support for export cipher suites and generate a unique 2048-bit Diffie-Hellman group. We have published a Guide to Deploying Diffie-Hellman for TLS with step-by-step instructions. If you use SSH, you should upgrade both your server and client installations to the most recent version of OpenSSH, which prefers Elliptic-Curve Diffie-Hellman Key Exchange.