Configuring TCP fin-no-ack Attack Screen
This topic describes how to configure detection of TCP fin-no-ack attack. A TCP header with the FIN flag set but not
the ACK flag is anomalous TCP behavior.
To enable detection of FIN bits with no ACK bit IDS option:
- Configure interfaces and assign an IP address to interfaces.
[edit] user@host# set interfaces ge-0/0/1 unit 0 family inet address 192.0.2.0/24 user@host# set interfaces ge-0/0/3 unit 0 family inet address 198.51.100.0/24
- Configure security zones trustZone and untrustZone and assign interfaces
to them.
[edit] user@host# set security zones security-zone trustZone host-inbound-traffic system-services all user@host# set security zones security-zone trustZone host-inbound-traffic protocols all user@host# set security zones security-zone trustZone interfaces ge-0/0/1.0 user@host# set security zones security-zone untrustZone host-inbound-traffic system-services all user@host# set security zones security-zone untrustZone host-inbound-traffic protocols all user@host# set security zones security-zone untrustZone interfaces ge-0/0/3.0
- Configure security policies from untrustZone to trustZone.
[edit] user@host# set security policies from-zone untrustZone to-zone trustZone policy policy1 match source-address any user@host# set security policies from-zone untrustZone to-zone trustZone policy policy1 match destination-address any user@host# set security policies from-zone untrustZone to-zone trustZone policy policy1 match application any user@host# set security policies from-zone untrustZone to-zone trustZone policy policy1 then permit user@host# set security policies default-policy deny-all
- Configure security screens and attach them to untrustZone.
[edit] user@host# set security screen ids-option untrustScreen tcp fin-no-ack user@host# set security zones security-zone untrustZone screen untrustScreen user@host# set security screen ids-option untrustScreen alarm-without-drop
- Configure syslog.
[edit] user@host# set system syslog file syslog any any user@host# set system syslog file syslog archive size 10000000 user@host# set system syslog file syslog structured-data user@host# set security policies from-zone untrustZone to-zone trustZone policy policy1 then log session-init user@host# set security policies from-zone untrustZone to-zone trustZone policy policy1 then log session-close
- Commit the configuration.
[edit] user@host# commit