Brian Atkins wrote:
Jason and John,
Again, thanks for the responses. I've finally had an opportunity to dig back into it after a rather nightmare-ish week...
I tried a couple of different things, without much success. First, seeing as how I'm realtively new at this, I went back to the docs on Netfilter and pulled a script out of the appedices of one of the HOWTOs and modified it for my use. Following their setup, I used it to create several new chains and new rules that I hadn't thought of implementing. Now, when I went back and checked out ip_tables_names and ip_tables_targets, I get the following:
root@fw>cat /proc/net/ip_tables_names mangle nat filter
root@fw>cat /proc/net/ip_tables_targets REJECT LOG DNAT SNAT
Also, I checked out the kernel config and got the following list of modules that were created with the new build:
root@fw>grep _NF_ /usr/src/linux/.config
CONFIG_IP_NF_CONNTRACK=m
# CONFIG_IP_NF_CT_ACCT is not set
# CONFIG_IP_NF_CONNTRACK_MARK is not set
# CONFIG_IP_NF_CT_PROTO_SCTP is not set
CONFIG_IP_NF_FTP=m
# CONFIG_IP_NF_IRC is not set
# CONFIG_IP_NF_TFTP is not set
# CONFIG_IP_NF_AMANDA is not set
# CONFIG_IP_NF_QUEUE is not set
CONFIG_IP_NF_IPTABLES=m
CONFIG_IP_NF_MATCH_LIMIT=m
CONFIG_IP_NF_MATCH_IPRANGE=m
CONFIG_IP_NF_MATCH_MAC=m
CONFIG_IP_NF_MATCH_PKTTYPE=m
CONFIG_IP_NF_MATCH_MARK=m
CONFIG_IP_NF_MATCH_MULTIPORT=m
CONFIG_IP_NF_MATCH_TOS=m
CONFIG_IP_NF_MATCH_RECENT=m
CONFIG_IP_NF_MATCH_ECN=m
CONFIG_IP_NF_MATCH_DSCP=m
CONFIG_IP_NF_MATCH_AH_ESP=m
CONFIG_IP_NF_MATCH_LENGTH=m
CONFIG_IP_NF_MATCH_TTL=m
CONFIG_IP_NF_MATCH_TCPMSS=m
CONFIG_IP_NF_MATCH_HELPER=m
CONFIG_IP_NF_MATCH_STATE=m
CONFIG_IP_NF_MATCH_CONNTRACK=m
CONFIG_IP_NF_MATCH_OWNER=m
CONFIG_IP_NF_MATCH_ADDRTYPE=m
CONFIG_IP_NF_MATCH_REALM=m
# CONFIG_IP_NF_MATCH_SCTP is not set
CONFIG_IP_NF_MATCH_COMMENT=m
# CONFIG_IP_NF_MATCH_HASHLIMIT is not set
CONFIG_IP_NF_FILTER=m
CONFIG_IP_NF_TARGET_REJECT=m
CONFIG_IP_NF_TARGET_LOG=m
CONFIG_IP_NF_TARGET_ULOG=m
CONFIG_IP_NF_TARGET_TCPMSS=m
CONFIG_IP_NF_NAT=m
CONFIG_IP_NF_NAT_NEEDED=y
CONFIG_IP_NF_TARGET_MASQUERADE=m
CONFIG_IP_NF_TARGET_REDIRECT=m
CONFIG_IP_NF_TARGET_NETMAP=m
CONFIG_IP_NF_TARGET_SAME=m
CONFIG_IP_NF_NAT_SNMP_BASIC=m
CONFIG_IP_NF_NAT_FTP=m
CONFIG_IP_NF_MANGLE=m
CONFIG_IP_NF_TARGET_TOS=m
CONFIG_IP_NF_TARGET_ECN=m
CONFIG_IP_NF_TARGET_DSCP=m
CONFIG_IP_NF_TARGET_MARK=m
CONFIG_IP_NF_TARGET_CLASSIFY=m
CONFIG_IP_NF_RAW=m
CONFIG_IP_NF_TARGET_NOTRACK=m
CONFIG_IP_NF_ARPTABLES=m
CONFIG_IP_NF_ARPFILTER=m
CONFIG_IP_NF_ARP_MANGLE=m
Likewise, here is what is currently loaded:
root@fw>lsmod
Module Size Used by
ip_nat_ftp 3584 0
ip_conntrack_ftp 72976 1 ip_nat_ftp
ipt_state 2560 5
ipt_limit 3072 2
iptable_mangle 3328 0
ipt_REJECT 6528 1
ipt_LOG 7552 2
iptable_nat 23868 2 ip_nat_ftp
ip_conntrack 49992 4 ip_nat_ftp,ip_conntrack_ftp,ipt_state,iptable_nat
iptable_filter 3328 1
ip_tables 23296 7 ipt_state,ipt_limit,iptable_mangle,ipt_REJECT,ipt_LOG,iptable_nat,iptable_filter
BLADABLADABLADA
Here is my routing table (for what it's worth):
root@fw>route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
[OUTSIDE _NET] * 255.255.255.192 U 0 0 0 eth0
[INSIDE_NET] * 255.0.0.0 U 0 0 0 eth2
loopback localhost 255.0.0.0 UG 0 0 0 lo
default [OUTSIDE_GW] 0.0.0.0 UG 0 0 0 eth0
And, finally, my current ruleset (and I welcome all critiques):
root@fw>iptables-save
# Generated by iptables-save v1.3.1
*mangle
:PREROUTING ACCEPT [4431:597383]
:INPUT ACCEPT [4387:587673]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [1709:222042]
:POSTROUTING ACCEPT [1686:202254]
COMMIT
*nat
:PREROUTING ACCEPT [2731:449771]
:POSTROUTING ACCEPT [13:950]
:OUTPUT ACCEPT [13:950]
-A PREROUTING -d [PUBLIC_IP] -i eth0 -j DNAT --to-destination [PRIVATE_IP]
-A PREROUTING -d [PUBLIC_IP] -i eth0 -j DNAT --to-destination [PRIVATE_IP]
-A POSTROUTING -s [PRIVATE_IP] -o eth0 -j SNAT --to-source [PUBLIC_IP]
-A POSTROUTING -s [PRIVATE_IP] -o eth0 -j SNAT --to-source [PUBLIC_IP]
COMMIT
*filter
:ALLOWED - [0:0]
:BAD_TCP_PACKETS - [0:0]
:ICMP_PACKETS - [0:0]
:INPUT DROP [2625:435028]
:FORWARD DROP [0:0]
:OUTPUT DROP [23:19788]
:POSTROUTING - [0:0]
:PREROUTING - [0:0]
:TCP_PACKETS - [0:0]
:UDP_PACKETS - [0:0]
-A ALLOWED -p tcp -m tcp --tcp-flags SYN,RST,ACK SYN -j ACCEPT
-A ALLOWED -p tcp -m state --state RELATED,ESTABLISHED -j ACCEPT
-A ALLOWED -p tcp -j DROP
-A BAD_TCP_PACKETS -p tcp -m tcp --tcp-flags SYN,ACK SYN,ACK -m state --state NEW -j REJECT --reject-with tcp-reset
-A BAD_TCP_PACKETS -p tcp -m tcp ! --tcp-flags SYN,RST,ACK SYN -m state --state NEW -j DROP
-A ICMP_PACKETS -s [PRIVATE_NET]/255.0.0.0 -p icmp -j ACCEPT
-A ICMP_PACKETS -s [PUBLIC_NET]/255.255.255.192 -p icmp -j ACCEPT
-A ICMP_PACKETS -s 127.0.0.0/255.0.0.0 -p icmp -j ACCEPT
-A ICMP_PACKETS -p icmp -m icmp --icmp-type 3/4 -j ACCEPT
-A INPUT -j PREROUTING
-A INPUT -p tcp -j BAD_TCP_PACKETS
-A INPUT -s 127.0.0.1 -i lo -j ACCEPT
-A INPUT -s [PRIVATE_IP_FW] -i lo -j ACCEPT
-A INPUT -s [PUBLIC_IP_FW] -i lo -j ACCEPT
-A INPUT -d [PUBLIC_IP_FW] -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -j TCP_PACKETS
-A INPUT -p udp -j UDP_PACKETS
-A INPUT -p icmp -j ICMP_PACKETS
-A FORWARD -p tcp -j BAD_TCP_PACKETS
-A FORWARD -d [PUBLIC_NET]/255.255.255.192 -p tcp -j PREROUTING
-A FORWARD -p icmp -m icmp --icmp-type 3/4 -j ICMP_PACKETS
-A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -m limit --limit 3/min --limit-burst 3 -j LOG --log-prefix "IPT FORWARD packet died: " --log-level 7
-A OUTPUT -s 127.0.0.1 -j ACCEPT
-A OUTPUT -s [PRIVATE_IP_FW] -j ACCEPT
-A OUTPUT -s [PUBLIC_IP_FW] -j ACCEPT
-A OUTPUT -m limit --limit 3/min --limit-burst 3 -j LOG --log-prefix "IPT OUTPUT packet died: " --log-level 7
-A TCP_PACKETS -p tcp -m tcp --dport 21 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 22 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 25 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 80 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 443 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 873 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 1999 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 4899 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 5666 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 8080 -j ALLOWED
-A TCP_PACKETS -p tcp -m tcp --dport 11371 -j ALLOWED
-A UDP_PACKETS -p udp -m udp --sport 53 -j ACCEPT
-A UDP_PACKETS -p udp -m udp --sport 123 -j ACCEPT
-A UDP_PACKETS -p udp -m udp --sport 873 -j ACCEPT
COMMIT
# Completed
I also tried FireHOL to build the rules from a config file. I liked how *through* it appeared to be, but I went back to the original script for troubleshooting purposes.
Now, even more strange is that I stripped everything out right down to just the natting piece and I still can't traverse the fw:
# Generated by iptables-save v1.3.1 on Fri May 20 06:23:40 2005 *raw :PREROUTING ACCEPT [185327:123272626] :OUTPUT ACCEPT [71616:17819696] COMMIT # Completed on Fri May 20 06:23:40 2005 # Generated by iptables-save v1.3.1 on Fri May 20 06:23:40 2005 *nat :PREROUTING ACCEPT [20964:3942558] :POSTROUTING ACCEPT [54:3564] :OUTPUT ACCEPT [53:3480] -A PREROUTING -d [PUBLIC_IP] -i eth0 -j DNAT --to-destination [PRIVATE_IP] -A PREROUTING -d [PUBLIC_IP] -i eth0 -j DNAT --to-destination [PRIVATE_IP] -A POSTROUTING -s [PRIVATE_IP] -o eth0 -j SNAT --to-source [PUBLIC_IP] -A POSTROUTING -s [PRIVATE_IP] -o eth0 -j SNAT --to-source [PUBLIC_IP] COMMIT # Completed on Fri May 20 06:23:40 2005 # Generated by iptables-save v1.3.1 on Fri May 20 06:23:40 2005 *filter :INPUT ACCEPT [955:375232] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [1219:191838] :POSTROUTING - [0:0] :PREROUTING - [0:0] -A FORWARD -i eth1 -j POSTROUTING COMMIT # Completed on Fri May 20 06:23:40 2005
By all intents I should be vulnerable to the world. From the outside, I can hit the external facing NIC, but I can't get to the public IP of one of my webservers. From the inside, I can hit both NICs (inside/outside) on the firewall, but not the internal facing NIC on the ex-router. From the firewall, I can see both WWW and my internal network.
Is there a tool to debug iptables to see if any of the rules are being used by incoming traffic?
-- Brian Atkins IT Services The Library Corporation http://TLCdelivers.com Ph: 800.624.0559
