I've enabled both SSH and HTTP in ufw. Using Linode VPS with Ubuntu 16.04.
After doing sudo ufw enable, I'm effectively locked out except for the virtual console which I can access via web browser.
Here's my listening daemons:
sudo netstat -lvpnut
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 4387/mysqld
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 4385/sshd
tcp6 0 0 :::80 :::* LISTEN 11543/apache2
tcp6 0 0 :::22 :::* LISTEN 4385/sshd
Once I disable ufw, I can ssh back in.
Here's sudo ufw status verbose with ufw enabled:
Status: active
Logging: on (low)
Default: deny (incoming), allow (outgoing), disabled (routed)
New profiles: skip
To Action From
-- ------ ----
22 ALLOW IN Anywhere
80 ALLOW IN Anywhere
22 (v6) ALLOW IN Anywhere (v6)
80 (v6) ALLOW IN Anywhere (v6)
Here's my output of iptables -nvL:
Chain INPUT (policy DROP 1 packets, 60 bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain DOCKER (0 references)
pkts bytes target prot opt in out source destination
Chain DOCKER-ISOLATION (0 references)
pkts bytes target prot opt in out source destination
2360 18M RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain ufw-after-forward (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-after-input (0 references)
pkts bytes target prot opt in out source destination
0 0 ufw-skip-to-policy-input udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:137
0 0 ufw-skip-to-policy-input udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:138
0 0 ufw-skip-to-policy-input tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:139
0 0 ufw-skip-to-policy-input tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:445
0 0 ufw-skip-to-policy-input udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:67
0 0 ufw-skip-to-policy-input udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:68
0 0 ufw-skip-to-policy-input all -- * * 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type BROADCAST
Chain ufw-after-logging-forward (0 references)
pkts bytes target prot opt in out source destination
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 LOG flags 0 level 4 prefix "[UFW BLOCK] "
Chain ufw-after-logging-input (0 references)
pkts bytes target prot opt in out source destination
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 LOG flags 0 level 4 prefix "[UFW BLOCK] "
Chain ufw-after-logging-output (0 references)
pkts bytes target prot opt in out source destination
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 LOG flags 0 level 4 prefix "[UFW ALLOW] "
Chain ufw-after-output (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-before-forward (0 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 3
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 4
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 11
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 12
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 8
0 0 ufw-user-forward all -- * * 0.0.0.0/0 0.0.0.0/0
Chain ufw-before-input (0 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
0 0 ufw-logging-deny all -- * * 0.0.0.0/0 0.0.0.0/0 ctstate INVALID
0 0 DROP all -- * * 0.0.0.0/0 0.0.0.0/0 ctstate INVALID
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 3
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 4
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 11
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 12
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmptype 8
0 0 ACCEPT udp -- * * 0.0.0.0/0 0.0.0.0/0 udp spt:67 dpt:68
0 0 ufw-not-local all -- * * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT udp -- * * 0.0.0.0/0 224.0.0.251 udp dpt:5353
0 0 ACCEPT udp -- * * 0.0.0.0/0 239.255.255.250 udp dpt:1900
0 0 ufw-user-input all -- * * 0.0.0.0/0 0.0.0.0/0
Chain ufw-before-logging-forward (0 references)
pkts bytes target prot opt in out source destination
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW AUDIT] "
Chain ufw-before-logging-input (0 references)
pkts bytes target prot opt in out source destination
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW AUDIT] "
Chain ufw-before-logging-output (0 references)
pkts bytes target prot opt in out source destination
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW AUDIT] "
Chain ufw-before-output (0 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- * lo 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
0 0 ufw-user-output all -- * * 0.0.0.0/0 0.0.0.0/0
Chain ufw-logging-allow (0 references)
pkts bytes target prot opt in out source destination
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 LOG flags 0 level 4 prefix "[UFW ALLOW] "
Chain ufw-logging-deny (2 references)
pkts bytes target prot opt in out source destination
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 ctstate INVALID LOG flags 0 level 4 prefix "[UFW AUDIT INVALID] "
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 LOG flags 0 level 4 prefix "[UFW BLOCK] "
Chain ufw-not-local (1 references)
pkts bytes target prot opt in out source destination
0 0 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
0 0 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type MULTICAST
0 0 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type BROADCAST
0 0 ufw-logging-deny all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 10
0 0 DROP all -- * * 0.0.0.0/0 0.0.0.0/0
Chain ufw-reject-forward (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-reject-input (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-reject-output (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-skip-to-policy-forward (0 references)
pkts bytes target prot opt in out source destination
0 0 DROP all -- * * 0.0.0.0/0 0.0.0.0/0
Chain ufw-skip-to-policy-input (7 references)
pkts bytes target prot opt in out source destination
0 0 DROP all -- * * 0.0.0.0/0 0.0.0.0/0
Chain ufw-skip-to-policy-output (0 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0
Chain ufw-track-forward (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-track-input (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-track-output (0 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 ctstate NEW
0 0 ACCEPT udp -- * * 0.0.0.0/0 0.0.0.0/0 ctstate NEW
Chain ufw-user-forward (1 references)
pkts bytes target prot opt in out source destination
Chain ufw-user-input (1 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22
0 0 ACCEPT udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:22
0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80
0 0 ACCEPT udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:80
Chain ufw-user-limit (0 references)
pkts bytes target prot opt in out source destination
0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 5 LOG flags 0 level 4 prefix "[UFW LIMIT BLOCK] "
0 0 REJECT all -- * * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable
Chain ufw-user-limit-accept (0 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0
Chain ufw-user-logging-forward (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-user-logging-input (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-user-logging-output (0 references)
pkts bytes target prot opt in out source destination
Chain ufw-user-output (1 references)
pkts bytes target prot opt in out source destination
What am I doing wrong?
Best Answer
This is likely because ufw is blocking the VPS connection to the NBD (Network Block Device), which causes the server to crash. I'm using scaleway as my VPS provider and had the same issue. Check out https://community.online.net/t/how-to-configures-iptables-with-input-rules-with-dynamic-nbd/303/22 to prevent this.