Ubuntu Servers :: Iptables To Rate-limit Brute Force Attacks On SSH Server?
Sep 30, 2010
I have a SSH server set up at home listening on port 22. I have hardened the server so it is pretty secure but I want to make it even safer by editing my iptables to rate-limit incoming connections and DROP false login attempts. I have tried these tutorials but I just cant get it to work:[URL]I want the debian-administration.org tutorial to work but when I try to add the first rule in terminal:sudo iptables -I INPUT -p tcp --dport 22 -i eth0 -m state --state NEW -m recent --setI get the following:Bad argument --set'I am new to iptables and I'm not sure if I'm doing something wrong when I try to set it up. I'm using Ubuntu 10.04.1 LTS with iptables v1.4.4.
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May 6, 2011
I am ashamed that I am causing other people troubles, but apparantly my server is involved in attacking the servers of other people.
I have to admit that I am not too familiar with using a CLI, or Linux for that matter, but I have a Debian server running under Plesk 10, which is colocated.
Now I have received messages from the datacenterm which state that my server is involved in brute force attacks.
The messages show a lot of lines like this:
Code:
The only I get from my hoster is to back up all domains and re-install the machine.
I want to resolve this asap, but do not agree with that action for two reasons: the machine just had a fresh re-install 2 months ago, so if it is a flaw in the OS, I will get the same flaw back, and if it is not OS related but due to a domain, I will get the problem back by putting back the backed-up domains.
But now I'm stuck: what steps should I follow to try and find the cause of this evil and make sure that my machine will not bother other machines anymore?
I realize that this probably will be a steep learning-curve, but please bare with me and help me to resolve this.
What have I done so far?
1) There are a number of live sites on this server, either running WordPress or Joomla, I have made sure they are all updated to the latest release.
2) I have manually looked at the source code of the index-files of those sites, haven't seen anything strange, like redirects.
3) I have used online scanners to check all sites for malware, all have been reported back to be clean.
4) I have run the Plesk-version of RKhunter, and that gives me certain warnings which I cannot (or do not) understand:
Code:
Code:
Code:
I received the first report of these attempts about a week ago and immediately changed the Plesk/SSH password to a 200bit password generated with KeePass, hoping that would keep out any evildoers.
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Mar 31, 2011
I have a mail server running RHEL, with postfix, dovecot, etc. I installed Fail2ban and this works wonders against SSH brute force attacks. It'll ban an IP address for a period of time if it unsuccessfully attempts to log on 3 times within, say a minute. I was wondering if it can be as effective with pop3 attacks. If it is, how can I get it done?
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Apr 8, 2010
I'm a newbie in the world of netfilter/iptables. I've read an article about iptables and rate limit module:
Code: iptables -A INPUT -p ICMP --icmp-type echo-request -m limit --limit 1/minute --limit-burst 5 -j ACCEPT The firewall will let the first 5 packets in in the first minute, -limit-burst 5; this means, however, that the packets/minute now is 5, so any further packets are blocked until packets/minute = 1, i.e. 5 minutes later. In the sixth minute, packets/minute will be 5/6 < 1, so another ping request will be let in. When the extra ping request is admitted, the ratio becomes 6/6 = 1 again, and packets are DROPped again until the next minute.
Now I have some problems in understanding how it works.
For example: I want ping google.com in this way: the kernel firewall permits to send the first 5 packet to google.com (--limit-burst 5) and then it blocks the remaining packets for 5 minutes. At sixth minute (because I wish a limit rate equal to 1/minute: --limit 1/minute) one packet can send to google again. And so on.
So my rule should be:
Code: iptables -A OUTPUT -d url_of_google -p icmp --icmp-type echo-request -m limit --limit 1/minute --limit-burst 5 -j ACCEPT In this way, if i digit
Code: ping -f url_of_gogle I expect that the first 5 packets are accepted (and so zero '.' will print on the screen) and then for the remaining 5 minutes no one packets will be accepted (and so a long string of '.' will print). But it doesn't work...
In man pages of ping we read (about -f option):
-f Flood ping. Outputs packets as fast as they come back or one hundred times per second, whichever is more. For every ECHO_REQUEST sent a period ``.'' is printed, while for every ECHO_REPLY received a backspace is printed. This provides a rapid display of how many packets are being dropped.
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Apr 26, 2011
My server has been the repeated victim of bandwidth attacks: any large file on the server is downloaded repeatedly, with the goal of pushing the server over the provider's bandwidth limit. How can I lessen the effect of these kinds of attacks with IPTables or APF? For example, can I set the server to: Is this possible? Is there a more effective way, and can a firewall even do this? My web server is Lighttpd, perhaps I can place such a rule directly in its config?
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Nov 8, 2010
im looking for a good brute force program that has i gui. i used to use brutus on windows but now im only running ubuntu so i need to find one.
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Mar 29, 2011
I set up an ASUS WL-500gP with original ASUS firmware to my LAN with IP address 192.168.1.1. If I navigate to address [URL] in my Firefox address bar, an Authentication required window opens up asking for "User name: " and "Password: ". Correct "User name: " is "admin" and correct "Password: " is "pA55w0Rd". They work fine if I type them in manually to the Authentication required window, but for some reason I can't get in using the hydra with words.txt password file, which contains "pA55w0Rd":
Code:
[root@ ~]# cat words.txt
password
user
pA55w0Rd
[code]....
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Feb 19, 2010
In my Open-Suse server I have a script, where makepasswd output(by default it generates similar passwords: cGyTbqpr, tpJ1LA, 33EXdo) is redirected to mkpasswd(which uses DES by default) in order to generate salted hash of this previously generated password. I would like to test the strength of this system. I have a quad core CPU, and if I start John The Ripper like this(I want to use -incremental:all flag):
john -incremental:all passwd
..only one core is utilized at 100%. Is there a possibility to make all four cores to crack this password? Or is this possible only after reprogramming John The Ripper? Or what is the algorithm for generating passwords with with -incremental:all flag? I mean if John generates passwords randomly in brute-force mode, then it's smart to start four different John processes simultaneously because then one of those four will find the password firs
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Mar 6, 2011
I have about 5 machines that are under Ddos daily and I use rate-limit for Iptables to protect that and it works good.My UDP ports 20100 to 20400 are actually under Ddos so these are the commands I use:
Code:
A INPUT -p udp -m udp --dport 20100:20500 -m state --state NEW -m recent --set --name DEFAULT --rsource
[code]....
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Dec 27, 2010
Does anyone know a simple out of the box option to limit traffic by IP with iptables? Output to each connected IP should be limited to to 1.5Mbps but I don;t want to limit incoming connections from the web. Ideally something with a tutorial because the LARC papers and stuff are impossible to read. For example, the user connects by VPN and requests the webpage [URL]. This should be sent to them at 1.5Mbs but if user 2 connects to [URL], this should also be sent at 1.5Mbps but the incoming ..... connection needs to be allowed to be unlimited to prevent incoming throttling..
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May 14, 2010
I am trying to limit bandwidth of certain ip addresses on my server. I have been doing hours of reading and not getting very far... So far I believe the iptables command is
ptables -A PREROUTING -s 178.33.23.44 -t mangle -j MARK --set-mark 2
ptables -A PREROUTING -s 178.33.23.45 -t mangle -j MARK --set-mark 2
ptables -A PREROUTING -s 178.33.23.46 -t mangle -j MARK --set-mark 2
ptables -A PREROUTING -s 178.33.23.47 -t mangle -j MARK --set-mark 2
and now I just need the tc command to read those marks and limit bandwidth, I have a gigabit connection and would like to limit each of these ip addresses to 10mbit in and out.
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Dec 23, 2010
I'm trying to limit access to port 8443 on our server to 2 specific IP addresses. For some reason, access is still being allowed even though I drop all packets that aren't from the named IP addresses. The default policy is ACCEPT on the INPUT chain and this is how we want to keep it for various reasons I wont get into here. Here's the output from iptables -vnL
[Code]...
Note the actual IP we are using is masked here with 123.123.123.123. Until I can get everything working properly, we're only allowing access from 1 IP instead of 2. We can add the other one once it all works right. I haven't worked with iptables very much. So I'm quite confused about why packets matching the DROP criteria are still being allowed.
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May 30, 2010
I have a linux box running between my router and my LAN. My connection speed is 10MB download and 1MB upload. The issue is that whenever someone starts to upload something, it is like my connection is down. No one else can open websites, read emails etc.Is it possible to place a limit for upload, maybe 50kb/s? This way, people won't use the entire upload speed available.
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Feb 4, 2011
I see on my webserver some logs as follows Quote:
203.252.157.98 - :25:02 "GET //phpmyadmin/ HTTP/1.1" 404 393 "-" "Made by ZmEu @ WhiteHat Team - www.whitehat.ro"
203.252.157.98 - :25:03 "GET //phpMyAdmin/ HTTP/1.1" 404 394 "-" "Made by ZmEu @
[code]....
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Jan 1, 2011
With Azureus/Vuze, can we set an upload/download rate limit depending on the time of day?
If not, do you know a torrent client allowing this? Client must be available on Linux.
I learned that you can install plugins for Azureus/Vuze. There is one about scheduling. I've tried to install it but I got a NullPointerException.
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May 20, 2011
I'd like to discourage the SSH bots that try to log into my system (CentOSv5), and among other things, I've changed my SSH port to someting other than 22. As well, I've been playing around with the idea of some iptables rules (note port 22 is used here as example):
Code:
# Allow SSH with a rate limit
iptables -A INPUT -i ppp0 -p tcp --syn --dport 22 -m hashlimit --hashlimit 15/hour --hashlimit-burst 3 --hashlimit-htable-expire 600000 --hashlimit-mode srcip --hashlimit-name ssh -j ACCEPT
iptables -A INPUT -i ppp0 -p tcp --syn --dport 22 -j LOG --log-prefix "[DROPPED SSH]: "
iptables -A INPUT -i ppp0 -p tcp --syn --dport 22 -j DROP
I am *NOT* an iptables expert. What do you all think about the above code snip?
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Apr 12, 2010
I'm thinking about some ways to limit access to my web-server. It runs Nginx and php in FCGI. The server contains a large amount of information. The data is freely available and no authentication is required but other companies might like to mirror it and use on their own servers.
The requests could be limited on different levels: IP, TCP, HTTP (by nginx) or by the php application. I found some solutions (like Nginx's limit_req_zone directive), but they do not solve the second part of the problem: there's no way to define a whitelist of clients who are allowed to use the data.
I thought about an intellectual firewall that would limit the requests on IP basis, but I'm yet to find such device. Another way was to hack some scripts that would parse the log file every minute and modify the iptables to ban suspicious IPs. It would take days and I doubt this system will survive, say, 1000 requests per second.
Perhaps, some HTTP proxy, like Squid, could do this?
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Feb 1, 2011
I am using ssh server to connect to my Ubuntu desktop. I opened the file sshd_config and change my port number of the server.I want to put a limit on the number of clients in the ssh server.
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Oct 27, 2010
I have a bridged network setup ifconfig -a gives following output
Code:
br0 Link encap:Ethernet HWaddr 00:26:b9:82:42:38
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::226:b9ff:fe82:4238/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:150779 errors:0 dropped:0 overruns:0 frame:0
[Code]...
3) What are these vmnet1,vmnet2,vmnet3,vmne4 which I see above. I used kvm and virt-manager to create a bridged setup.
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Nov 3, 2010
Take this scenario If I have rate limited the connections to 4.(i.e if you attempt 4th connection you wont be able to login for some time.) If in a minute I get disconnected 3 times while I was already logged in on the server with a screen session, will I be able to login or I need to keep quite for a minute?
Quote:
-A INPUT -i eth0 -p tcp -m tcp --dport 22 -m state --state NEW -m recent --update --seconds 60 --hitcount 4 --name DEFAULT --rsource -j DROP
-A INPUT -i eth0 -p tcp -m tcp --dport 22 -m state --state NEW -m recent --set --name DEFAULT --rsource
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May 14, 2011
I'm trying to limit the number of the ICMP packets reaching my server, so I'm using the limit module of iptables, unfortunately it seems the limit I set is totally ignored as I can easily send tens of ICMP packets and get a reply in less than 0.3 second Quote:
m3xican@m3xtop:~$ sudo ping -i0 -c20 x.x.x.x 20 packets transmitted, 20 received, 0% packet loss, time 230ms
rtt min/avg/max/mdev = 184.969/185.895/189.732/1.301 ms, pipe 16, ipg/ewma 12.138/186.232 ms This is the rule I'm using to accept ICMP packets (default setting is DROP)
Code:
iptables -A INPUT -p icmp -m limit --limit 1/s -j ACCEPT
And these are the kernel modules related to iptables
Code:
Module Size Used by
xt_limit 1382 0
[Code]...
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May 12, 2010
I have a VPS server with 512 MB memory. The php.ini is set so script memory limit = 16 MB. However, I have noticed in my top report, instances like the following:
Quote:
5484 coldclim 25 0 46476 32m 5920 R 0.0 6.4 0:00.93 php
The bold number of 6.4 is the % of sever memory this process is using. 6.4 % of 512 MB of memory is about 32 MB of memory, so it appears that this isn't being limited by php.ini. Am I correct? This leads to the next question: Is there some way to limit the amount of memory a single suphp process can use? (Basically, something like the setting in php.ini which limits suphp processes in the same way.)
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Feb 24, 2010
I have a linux firewall. I want to limit a ssh connection number from local network to internet .
Example :
Internal pc (192.168.0.10) start a ssh scan to the external (internet) host.
I want that iptables limit that host (192.168.0.10) and block ssh connection from this host at 3 attempt.
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Jan 11, 2011
I am at a loss how to prevent Denial of Service attacks to port 25 and not block legitimate connections from 2 Barracuda 800(s) and block smart phones such as iPhones/Blackberrys/iPhones that use the server smtp.server.com for email.
Presently for port 25
RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 25 -j ACCEPT
The 2 Barracuda 800(s) make port 25 connections all the time, plus users with smart_phones have the incoming server type:
IMAP
pop.server.com
smtp.server.com
Is there a way to keep Denial of Service attacks from happening with iptables rules without causing blocking to the Barracuda(s) that make constant port 25 connections & smart phones that poll? I was thinking if I allowed the Barracuda(s) in these lines
-s (barracuda)24.xx.xx.xx -d (emailserver)24.00.xx.xx -p tcp -m tcp --dport 25 -m state --state NEW -j ACCEPT
Where the source would be the Barracuda going to the email server. It would be allowed, then I am left with how to allow other connections like Smart_Phones that connect via Port 25. I am thinking if I put rules in place doing connection counts in a minute it would result in errors connecting to the server and people would start complaining. Plus any limiting may result in blocking real traffic. Then would I need to allow the ISP range in the above example to accept port 25, I am still left with how to drop a flood/denial of service attack.
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Apr 5, 2011
Can I, with only the use of IPTABLES, limit the incoming bandwith for a protocol? We have for example servers that have a FTP and HTTP server running and whenever HTTP has a lot of connections open, the other uploads/downloads get a timeout. I know I can limit the number of connections but prefer to limit on protocol level. Is this possible using IPTABLES and if so, can someone indicate how to proceed or provide a link? If it's not possible can someone point me to the right tool for the job?
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Mar 5, 2011
I am trying to make start an iptables.cf script on my server.
I have copied it into /etc/init.d/
And try to make it load with /etc/init.d/iptables.cf start
Then "not permission" (I was the root then).
So, sudo /etc/init.d/iptables.cf start
Then, "command not found".
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Apr 16, 2011
I am running Ubuntu server 10.10 and trying to setup iptables rules in /etc/if-up.d/iptables
Quote:
root@host# cat /etc/network/if-up.d/iptables
#!/bin/sh -e
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
Problem is that iptables doesn't get updated and I don't see them when iptables -L is executed after reboot.
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Nov 26, 2010
I am unable to restore my iptables from iptables-save after upgrading Fedora. I cannot get iptables-restore to work, and I have resorted to entering rules manually using the GUI.
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Apr 18, 2011
If there are users in a network who have desktop Linux (any variety), is there a way to configure their computers to "require" them to save documents to the network? Like for example, redirecting their /Home folders to a network file server or not allowing them to save files to their local hard drives?
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May 6, 2010
I have a server with 48 cores, 8 6-way Opteron CPU's. Ubuntu Server 9.04 only sees 32 processors. Is there a limit on the number of cores/processors that the server will use? Windows 2008 on the same server sees all 48 cores and the so does the BIOS, so this is unique to Ubuntu right now.
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