Hello Houman, You can do that. I wonder though why that is a problem. Are they providing a private subnet on the link of your server?
Kind regards Noel Am 14.10.19 um 12:03 schrieb Houman: > Hi Noel, > > That makes sense, thank you. > > I received a followup email from our server provider (about a new netscan > attempt from one of our users today). > > """ > We would recommend that you set up a local firewall and block outgoing > traffic to the following prefixes > https://tools.ietf.org/html/rfc1918 > > 10.0.0.0/8 <http://10.0.0.0/8> > > 172.16.0.0/12 <http://172.16.0.0/12> > > 192.168.0.0/16 <http://192.168.0.0/16> > Please block this range of RFC1918 on your server. > We would like to avoid further network abuse from your end. > """ > > Is this as simple as > > iptables -A FORWARD -d 10.0.0.0/8 <http://10.0.0.0/8> -j REJECT > iptables -A FORWARD -d 172.16.0.0/12 <http://172.16.0.0/12> -j REJECT > iptables -A FORWARD -d 192.168.0.0/16 <http://192.168.0.0/16> -j REJECT > > Or am I oversimplifying this? > > Many Thanks, > Houman > > > On Mon, 14 Oct 2019 at 13:02, Noel Kuntze <noel.kuntze@thermi.consulting> > wrote: > > Hello Houman, > > Depends on if you have a whitelist or blacklist rule set. > > With the ruleset you have provided in this email, you need to accept the > stuff you want. So up to 5 new connections per second. > > Kind regards > > Noel > > Am 14.10.19 um 10:40 schrieb Houman: > > Hi Noel, > > > > Actually based on my firewall config, I think I have to DROP it instead > of ACCEPT if it's over the 5/sec limit? Don't you agree? > > > > iptables -I FORWARD 2 -m conntrack --ctstate NEW -m hashlimit > --hashlimit-name NETSCAN --hashlimit-mode srcip --hashlimit-srcmask 32 > --hashlimit-above 5/s -j DROP > > > > So I replace *hashlimit-upto* with *hashlimit-above* following with a > DROP. > > > > This is my current firewall settings based on your previous suggestion. > If Iptables is clever enough to DROP the connection if hashlimit-upto is > exceeded, it should work as well. > > > > # iptables-save > > *filter > > :INPUT DROP [6374:460035] > > :FORWARD DROP [7119:2071794] > > :OUTPUT ACCEPT [19665335:23255290771] > > -A INPUT -i lo -j ACCEPT > > -A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT > > -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT > > -A INPUT -p tcp -m tcp --dport 2022 -j ACCEPT > > -A INPUT -p udp -m udp --dport 500 -j ACCEPT > > -A INPUT -p udp -m udp --dport 4500 -j ACCEPT > > -A FORWARD -s 10.10.0.0/17 <http://10.10.0.0/17> <http://10.10.0.0/17> > -d 10.10.0.0/17 <http://10.10.0.0/17> <http://10.10.0.0/17> -j DROP > > -A FORWARD -m conntrack --ctstate NEW -m hashlimit --hashlimit-upto > 5/sec --hashlimit-burst 5 --hashlimit-mode srcip --hashlimit-name NETSCAN -j > ACCEPT > > -A FORWARD -m policy --dir in --pol ipsec -j ACCEPT > > -A FORWARD -m policy --dir out --pol ipsec -j ACCEPT > > COMMIT > > # Completed on Mon Oct 14 08:30:14 2019 > > # Generated by iptables-save v1.6.1 on Mon Oct 14 08:30:14 2019 > > *nat > > :PREROUTING ACCEPT [222978690:20761159044] > > :INPUT ACCEPT [1143238:398065963] > > :OUTPUT ACCEPT [245876:24207759] > > :POSTROUTING ACCEPT [245876:24207759] > > -A POSTROUTING -s 10.10.0.0/17 <http://10.10.0.0/17> > <http://10.10.0.0/17> -o enp2s0 -m policy --dir out --pol ipsec -j ACCEPT > > -A POSTROUTING -s 10.10.0.0/17 <http://10.10.0.0/17> > <http://10.10.0.0/17> -o enp2s0 -j MASQUERADE > > COMMIT > > # Completed on Mon Oct 14 08:30:14 2019 > > # Generated by iptables-save v1.6.1 on Mon Oct 14 08:30:14 2019 > > *mangle > > :PREROUTING ACCEPT [76920955633:50815277695359] > > :INPUT ACCEPT [27612054762:8305407205459] > > :FORWARD ACCEPT [49298861266:42508240159831] > > :OUTPUT ACCEPT [34323442858:39692165780388] > > :POSTROUTING ACCEPT [83603096494:82195502934979] > > -A FORWARD -s 10.10.0.0/17 <http://10.10.0.0/17> <http://10.10.0.0/17> > -o enp2s0 -p tcp -m policy --dir in --pol ipsec -m tcp --tcp-flags SYN,RST > SYN -m tcpmss --mss 1361:1536 -j TCPMSS --set-mss 1360 > > COMMIT > > > > On Mon, 14 Oct 2019 at 11:14, Houman <hou...@gmail.com > <mailto:hou...@gmail.com> <mailto:hou...@gmail.com > <mailto:hou...@gmail.com>>> wrote: > > > > Hello Noel, > > > > Thanks for your solution, I just tried it: > > > > iptables -I FORWARD 2 -m conntrack --ctstate NEW -m hashlimit > --hashlimit-mode srcip --hashlimit-srcmask 32 --hashlimit-upto 5/s -j ACCEPT > > > > But I got this error message: > > > > iptables v1.6.1: hashlimit: option "--hashlimit-name" must be > specified > > > > I googled and added the missing name like this: > > > > iptables -I FORWARD 2 -m conntrack --ctstate NEW -m hashlimit > --hashlimit-name NETSCAN --hashlimit-mode srcip --hashlimit-srcmask 32 > --hashlimit-upto 5/s -j ACCEPT > > > > Do you agree with this approach to prevent VPN users from running > Netscans? > > > > Many Thanks, > > Houman > > > > > > On Wed, 31 Jul 2019 at 14:51, Noel Kuntze > <noel.kuntze@thermi.consulting> wrote: > > > > Hello Houman, > > > > A "netscan" attack isn't actually anything worthy of an abuse > email. > > It's not part of a benign usage pattern of a VPN service, but > it itself isn't illegal or anything. > > You can only slow down such scans by rate limiting the number > of new connections using the hashlimit match module, for example. > > > > E.g. -A FORWARD -m conntrack --ctstate NEW -m hashlimit > --hashlimit-mode srcip --hashlimit-srcmask 32 --hashlimit-upto 5/s -j ACCEPT > > > > Kind regards > > > > Noel > > > > Am 30.07.19 um 16:39 schrieb Houman: > > > Sorry I mistyped. I meant Netscan. > > > > > > The abuse message was saying: *NetscanOutLevel: Netscan > detected from xx.xx.xx.xx* > > > > > > This is possible though, that VPN users run a netscan and > scan the ports. Am I correct? > > > > > > Thanks, > > > > > > On Tue, 30 Jul 2019 at 15:30, Thor Simon > <thor.si...@twosigma.com <mailto:thor.si...@twosigma.com> > <mailto:thor.si...@twosigma.com <mailto:thor.si...@twosigma.com>> > <mailto:thor.si...@twosigma.com <mailto:thor.si...@twosigma.com> > <mailto:thor.si...@twosigma.com <mailto:thor.si...@twosigma.com>>>> wrote: > > > > > > I don't think netstat does what you think it does. It is > a _local_ tool. Perhaps the "abuse notification" you received is a phishing > attack? > > > > > > Hae a look at the manual page: > > > > > > > http://manpages.ubuntu.com/manpages/trusty/man8/netstat.8.html > > > > > > ________________________________ > > > From: Houman <hou...@gmail.com <mailto:hou...@gmail.com> > <mailto:hou...@gmail.com <mailto:hou...@gmail.com>> <mailto:hou...@gmail.com > <mailto:hou...@gmail.com> <mailto:hou...@gmail.com > <mailto:hou...@gmail.com>>>> > > > Sent: Jul 30, 2019 10:18 AM > > > To: users@lists.strongswan.org > <mailto:users@lists.strongswan.org> <mailto:users@lists.strongswan.org > <mailto:users@lists.strongswan.org>> <mailto:users@lists.strongswan.org > <mailto:users@lists.strongswan.org> <mailto:users@lists.strongswan.org > <mailto:users@lists.strongswan.org>>> > > > Subject: [strongSwan] How to block Netstat attacks from > VPN users? > > > > > > Hello, > > > > > > I had an interesting abuse notification that someone has > run a netstat through our VPN. > > > > > > > time protocol src_ip src_port > dest_ip dest_port > > > > > --------------------------------------------------------------------------- > > > > Tue Jul 30 13:38:01 2019 UDP 136.243.xxx.xxx 21346 => > 172.20.10.17 21346 > > > > Tue Jul 30 13:38:01 2019 UDP 136.243.xxx.xxx 21346 => > 172.20.10.19 21346 > > > > > > I was wondering if there is a good way to block all VPN > users from running hacker tools such as netstat (port scanning) altogether. > Is there a reliable way to do that with iptables? > > > > > > I came across this snippet that should block port scans, > but I'm not sure if that would block a VPN user after all since the VPN > traffic is masqueraded. > > > > > > iptables -A port-scan -p tcp --tcp-flags SYN,ACK,FIN,RST > RST -m limit --limit 1/s -j RETURN > > > iptables -A port-scan -j DROP --log-level 6 > > > iptables -A specific-rule-set -p tcp --syn -j syn-flood > > > iptables -A specific-rule-set -p tcp --tcp-flags > SYN,ACK,FIN,RST RST -j port-scan > > > > > > Any suggestions, please? > > > Many Thanks, > > > Houman > > > > > > > > > > > > > -- > > Noel Kuntze > > IT security consultant > > > > GPG Key ID: 0x0739AD6C > > Fingerprint: 3524 93BE B5F7 8E63 1372 AF2D F54E E40B 0739 AD6C > > > > > > -- > Noel Kuntze > IT security consultant > > GPG Key ID: 0x0739AD6C > Fingerprint: 3524 93BE B5F7 8E63 1372 AF2D F54E E40B 0739 AD6C > > -- Noel Kuntze IT security consultant GPG Key ID: 0x0739AD6C Fingerprint: 3524 93BE B5F7 8E63 1372 AF2D F54E E40B 0739 AD6C
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