A new attack named LogJam is targeting the cryptographic component named Diffie-Hellman, a means of securely exchanging cryptographic keys over a public channel. The severity of this attack is definitely lower than that of Heartbleed and is comparable to FREAK. The attack requires an active attacker positioned on the network path between the client and the server. The attacker can trick servers to use export grade (e.g. crackable) 512bit Diffie Hellman groups. This is only applicable to SSL with PFS enabled. The security community believes it to make global surveillance and eavesdropping more difficult.”]
Source: https://informationsecuritybuzz.com/articles/an-under-the-hood-look-at-logjam/