According to Juniper an attacker can blindly send packets that attempt to disturb or disrupt a TCP connection. "With a fast network connection an attacker can theoretically send forged packets that span the entire range of sequence numbers in a relatively short time period, essentially ensuring that an attack can succeed."
Affected products include: All Juniper M-series and T--series routers running software built prior to March 1, 2004; all Juniper E-series routers running software earlier than Release 5.2.1; all NetScreen firewalls running ScreenOS earlier than release 5.0R6.
For more go to http://www.juniper.net/support/alert.html