This type of attack has become very common lately. Here's a more specific example:
- The attacker decides to target IP address 127.0.0.1:27015, which is a CS:S server that he has been banned from.
- The attacker connects to a machine that he had previously compromised and uses a traffic generator tool to send simple query packets to a large number of other game servers, specifying a (fake) source of 127.0.0.1:27015. Each query packet is less than 50 bytes, so the attacker can send many thousands of these per second without using much bandwidth; even a very low-end machine can do it.
- These game servers ("reflectors") respond to 127.0.0.1:27015 with much larger packets, often 500+ bytes long, containing lists of their rules and connected players.
- The CS:S server at 127.0.0.1:27015, upon receiving the huge wave of attack traffic from thousands of different IPs, is overwhelmed. It is unable to serve legitimate clients or respond to queries itself, causing a denial of service.
Commonly, DRDoS attacks use Quake3, Wolfenstein:ET, CoD* servers, and other old Quake3-engine-based games as the reflectors. These games don't have facilities to limit query response rates and send large response packets, making them ideal for this purpose.
If you were linked to this post because you are being used as a reflector in order to attack an IP here, please understand that we are not actually sending the queries -- we are the victim that is being hit with responses from servers like yours. Your primary course of action should be to block that spoofed traffic from reaching your servers via an ACL. You could also try to find out the true source of this traffic by contacting your upstream and asking them to track down where the spoofed packets are coming from (and having them do the same with that provider). Most ISPs won't do this unless large sums and the FBI are involved, but it doesn't hurt to try.
If you run Q3/ET/CoD*/etc servers (any version) on Windows, this patch is one workaround: http://files.nfoe.net/cod4/CoD4_Getstatus_Flood_Fix.zip
If you run CoD4 servers (1.7) on Linux, the latest beta version of CoD4 is the way to go: http://treefort.icculus.org/cod/cod4-ln ... st.tar.bz2
If you run other Q3-engine games on Linux, and you have the "string", "hashlimit", and "recent" iptables kernel modules available, you can filter the traffic with rules like these:
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# add a host to the banlist and then drop the packet. iptables -N QUERY-BLOCK iptables -A QUERY-BLOCK -m recent --reap --seconds 30 iptables -A QUERY-BLOCK -m recent --set --name blocked-hosts -j DROP # is this a query packet? if so, block commonly attacked ports outright, # then see if it's a known attacking IP, then see if it is sending at a high # rate and should be added to the list of known attacking IPs. iptables -N QUERY-CHECK iptables -A QUERY-CHECK -p udp -m string ! --string "getstatus" --algo bm --from 32 --to 33 -j RETURN iptables -A QUERY-CHECK -p udp --sport 0:1025 -j DROP iptables -A QUERY-CHECK -p udp --sport 3074 -j DROP iptables -A QUERY-CHECK -p udp --sport 7777 -j DROP iptables -A QUERY-CHECK -p udp --sport 27015:27100 -j DROP iptables -A QUERY-CHECK -p udp --sport 25200 -j DROP iptables -A QUERY-CHECK -p udp --sport 25565 -j DROP # is it already blocked? continue blocking it and update the counter so it # gets blocked for at least another 30 seconds. iptables -A QUERY-CHECK -m recent --update --name blocked-hosts --seconds 30 --hitcount 1 -j DROP # check to see if it exceeds our rate threshold, # and add it to the list if it does. iptables -A QUERY-CHECK -m hashlimit --hashlimit-mode srcip --hashlimit-name getstatus --hashlimit-above 2/second -j QUERY-BLOCK # look at all the packets going to q3/cod*/et/etc servers iptables -A INPUT -p udp --dport 27960:29000 -j QUERY-CHECK
- By calling your upstream and having them apply an ACL to filter some of the source ports for you (a range from 27960-29000 to block common Q3-engine attacks, for instance).
- By using a Linux firewall on your side to block the remaining traffic, through the use of the "string" iptables module. Use a rule like this on the target machine:
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iptables -A INPUT -p udp -m string --string "statusResponse" --algo bm --from 32 --to 33 -j DROP