Syn Attach – 6 Months – Thousands Of Request A Second

For the last 6 months our site has been under severe brute force, syn flood attack. They keep bombarding a single URL of the server and it is xml file. They are not attacking any other URL.

We have removed the xml page from our site but still they keep on sending requests, this is for the last 6 months non stop.

The IP has been changed just to see and they are sending several thousand requests per second. The requests come from different IPS and different ranges, so you can not even block the IP’s. They seem to be coming from a legitimate IP’s.

Due to this I have had to pay for an extremely expensive server which holds 8 GB of RAM and quad core processor etc, however, even with this the server server still reaches critical level, just because these requests are eating up my resources.

Our technical team has been working on all aspects of apache server security, external modules, firewall, hardware firewall from beginning but still we are not able to stop them.

We have installed following modules.

4) mod_security

5) mod_evasive

6) Firewall

7) SYS_Cookies enabled

We have worked with the hosting company and their technical team leader, he installed the best CISCO hardware firewall and tried to stop them, but in vain.

We have checked our server to see if anything from our site is causing the request, no extra file uploaded on to the server. For example if some file has been upload or some text has been added to the file (checked if we’ve been hacked). Even though we checked for any hacks, I am still wondering if there is something we do not know about. Can a hack lead to huge amounts of traffic?

We need some help to stop these attacks. We have searched a lot and have found that sites that get attacked like this have only one option is to shut down till it stops. I really hope that will not be the case for us. Please let us know if any one has any ideas to deal with this.

Also could it be our own part of php code which can do this? We are ready to check every php file to make sure it does not have any line of code which can be dangerous?

We worked with hardware firewall company to drop a request on the spot coming for the single URL but it is getting setup.

We have antivirus running on server however if any specific antivirus or antimalware is needed, we can try that.

Following are the details I have got from my linux admin. This will help you to trace the issue in better way.
Problem: Apache SYN_RECV

OS - RHEL5
kernels - 2.6.18-92.1.22.el5-x86_64
2.6.18-92.el5-x86_64

rpms:-
kernel-devel-2.6.18-92.el5
kernel-headers-2.6.18-92.1.22.el5
kernel-devel-2.6.18-92.1.22.el5
kernel-2.6.18-92.1.22.el5
kernel-2.6.18-92.el5

OS Type:
cat /etc/issue
Red Hat Enterprise Linux Server release 5.2 (Tikanga)
> cat /proc/version
Linux version 2.6.18-92.1.22.el5 (mockbuild@hs20-bc2-5.build.redhat.com) (gcc version 4.1.2 20071124 (Red Hat 4.1.2-42)) #1 SMP Fri Dec 5 09:28:22 EST 2008

We are providing 403 code for the URL request.

netstat:

tcp 0 0 domain.com:http 85-156-91-20.elisa-mo:55168 SYN_RECV
tcp 0 0 domain.com:http 220.255.7.227:27183 SYN_RECV
tcp 0 0 domain.com:http 5e03cbc4.bb.sky.com:51086 SYN_RECV
tcp 0 0 domain.com:http 79.126.234.198:18139 SYN_RECV
tcp 0 0 domain.com:http 78.148.175.148:11115 SYN_RECV
tcp 0 0 domain.com:http 83-154-143-68.rev.lib:61479 SYN_RECV
tcp 0 0 domain.com:http ABTS-North-Static-248:54775 SYN_RECV
tcp 0 0 domain.com:http 90-230-131-95-no130.tb:1134 SYN_RECV
tcp 0 0 domain.com:http static-host119-73-6-2:49538 SYN_RECV
tcp 0 0 domain.com:http 222.127.130.238:gtp-control SYN_RECV
tcp 0 0 domain.com:http acl1-1571bts.gw.smartbr:g5m SYN_RECV
tcp 0 0 domain.com:http athedsl-282427.home.o:60002 SYN_RECV
tcp 0 0 domain.com:http CPE-58-166-77-138.nsw:60067 SYN_RECV
tcp 0 0 domain.com:http C-59-101-99-107.syd.c:51097 SYN_RECV
tcp 0 0 domain.com:http ti0111a380-2667.bb.on:60993 SYN_RECV
tcp 0 0 domain.com:http 92.81.2.242:60451 SYN_RECV
tcp 0 0 domain.com:http 118.100.120.248:pserver SYN_RECV
tcp 0 0 domain.com:http triband-del-59.178.84:50140 SYN_RECV
tcp 0 0 domain.com:http cpc4-leds5-0-0-cust82brpd SYN_RECV
tcp 0 0 domain.com:http ALyon-153-1-8-78.w86-:59494 SYN_RECV
tcp 0 0 domain.com:http 120.28.199.183:3comnetman SYN_RECV
tcp 0 0 domain.com:http h248.4.16.98.dynamic.:60758 SYN_RECV
tcp 0 0 domain.com:http 89.211.205.59:64217 SYN_RECV
tcp 0 0 domain.com:http CPE-124-187-26-30.qld:ff-sm SYN_RECV
tcp 0 0 domain.com:http frw.Gloworld.com:59104 SYN_RECV
tcp 0 0 domain.com:http 220.255.7.182:winpoplanmess SYN_RECV
tcp 0 0 domain.com:http srisaionline180.excell:1232 SYN_RECV
tcp 0 0 domain.com:http CPE-60-230-16-150.vic:52611 SYN_RECV
tcp 0 0 domain.com:http 203.82.91.102:41318 SYN_RECV
tcp 0 0 domain.com:http 69.171.165.50:32454 SYN_RECV
tcp 0 0 domain.com:http dsl-TN-static-195.:corbaloc SYN_RECV
tcp 0 0 domain.com:http 210.186.66.179:49330 SYN_RECV
tcp 0 0 domain.com:http ABTS-North-D:xinuexpansion3 SYN_RECV
tcp 0 0 domain.com:http c122-106-133-46.livrp:49273 SYN_RECV
tcp 0 0 domain.com:http 173.subnet125-1:nssalertmgr SYN_RECV
tcp 0 0 domain.com:http 121.246.52.30.dynamic:63977 SYN_RECV
tcp 0 0 domain.com:http mobile-3G-dyn-BC-179-1:4464 SYN_RECV
tcp 0 0 domain.com:http crd48.neoplus.adsl.t:aminet SYN_RECV


Following we have done till now is mentioned below for the configurations.

###############
sysctl.conf

##############
# Kernel sysctl configuration file for Red Hat Linux
#
# For binary values, 0 is disabled, 1 is enabled. See sysctl(8) and
# sysctl.conf(5) for more details.

# Controls IP packet forwarding
net.ipv4.ip_forward = 0

# Controls source route verification
net.ipv4.conf.default.rp_filter = 1

# Do not accept source routing
net.ipv4.conf.default.accept_source_route = 0

# Controls the System Request debugging functionality of the kernel
kernel.sysrq = 0

# Controls whether core dumps will append the PID to the core filename
# Useful for debugging multi-threaded applications
kernel.core_uses_pid = 1

# Controls the use of TCP syncookies
net.ipv4.tcp_syncookies = 1

# Controls the maximum size of a message, in bytes
kernel.msgmnb = 65536

# Controls the default maxmimum size of a mesage queue
kernel.msgmax = 65536

# Controls the maximum shared segment size, in bytes
kernel.shmmax = 68719476736

# Controls the maximum number of shared memory segments, in pages
kernel.shmall = 4294967296
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_synack_retries = 2
# Enable IP spoofing protection, turn on Source Address Verification
net.ipv4.conf.all.rp_filter = 1
# Enable TCP SYN Cookie Protection
net.ipv4.tcp_syncookies = 1

# 65536 seems to be the max it will take
net.ipv4.ip_conntrack_max = 1048576
net.ipv4.tcp_rmem = 4096 87380 8388608
net.ipv4.tcp_wmem = 4096 87380 8388608
net.core.rmem_max = 8388608
net.core.wmem_max = 8388608
net.core.netdev_max_backlog = 5000
net.ipv4.tcp_window_scaling = 1


#############
fwsnort, bfd burnintest chkrootkit ddos faf lsm nobody_check sim apf

#############
modsecurity-apache

LoadModule evasive20_module /usr/lib64/httpd/modules/mod_evasive20.so

<IfModule mod_evasive20.c>
DOSHashTableSize 3097
DOSPageCount 3
DOSSiteCount 50
DOSPageInterval 1
DOSSiteInterval 1
DOSBlockingPeriod 30
</IfModule>

LoadModule security_module /usr/lib64/httpd/modules/mod_security.so

<IfModule mod_evasive20.c>
DOSHashTableSize 3097
DOSPageCount 3
DOSSiteCount 50
DOSPageInterval 1
DOSSiteInterval 1
DOSBlockingPeriod 30
</IfModule>

####################