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Protecting TCP/IP stack is a very challenging task in a culture where easy access to information prevails over security concerns. The key problem here is that the need for an efficient enterprise to provide relatively unfettered access to data, combined with the highly decentralized nature of operations, is irrevocably connected with the potential for serious security breaches. Maintaining and, especially, improvement of large enterprises IT security is a huge challenge and introduction of new OSes like Linux is only one relatively minor problem among many others.
We sing out the following critical issues :
Network infrastructure and server complexity in the large enterprises has increased so
significantly that it has become a constraint on how flexible a business can be. Server
consolidation based on virtual machine concept in a large enterprise environment is the
necessity that no large enterprise can avoid. This movement already started in AIX space and
Windows space (sometimes under VMware, which is this case can be reused for Linux virtualization
purposes), but it will definitely accelerated in the future.
Linux's growing popularity is attracting unwanted attention from virus writers, script kiddies and criminal elements. In response, Linux advocates are putting a new emphasis on security measures and working to reassure large enterprises that the OS is secure for important enterprise applications.
Using different compiler to make application less susseptable to off-the-shelf exploits is one promising avenue. Recompiling such component as sendmail is easy.
Many exploits are complier dependent and the necessity to cover
both gcc and Sun Studio 10 compliers significantly complicates the creation
of working exploit. For example Intel compiler is definitely recommended for compiling
bind and Sendmail. Obscurity understood here as using less popular software platforms with some additional security features is a viable method
to secure any complex operating environment and being off the most popular (and
the most vulnerable) applications is always a plus.
route | grep link-locallink-local
*255.255.0.0 U 0
Then remove the avahi package and its dependencies
netstat -tanp | grep LISTEN
Typical output:[root ]# netstat -tanp | grep LISTEN
tcp 0 0 127.0.0.1:8000 0.0.0.0:* LISTEN 2256/nasdtcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 2166/mysqld
tcp 0 0 127.0.0.1:4690 0.0.0.0:* LISTEN 2376/prelude-managetcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN 2057/cupsd
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 2244/mastertcp 0 0 :::22 :::* LISTEN 2068/sshd
Locate the pid in the netstat commandcat /proc/<pid>/cmdline
If not full path, run which or locate to find utility
rpm -qf full-path-of-daemon
rpm -e package
If difficult to remove due to dependencies:
chkconfig <service> off
# Don't reply to broadcasts. Prevents joining a smurf attack
net.ipv4.icmp_echo_ignore_broadcasts = 1# Enable protection for bad icmp error messages
net.ipv4.icmp_ignore_bogus_error_responses = 1# Enable syncookies for SYN flood attack protection
net.ipv4.tcp_syncookies = 1# Log spoofed, source routed, and redirect packets
net.ipv4.conf.all.log_martians = 1net.ipv4.conf.default.log_martians = 1
# Don't allow source routed packetsnet.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0# Turn on reverse path filtering
net.ipv4.conf.all.rp_filter = 1net.ipv4.conf.default.rp_filter = 1
# Don't allow outsiders to alter the routing tablesnet.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0# Don't pass traffic between networks or act as a router
net.ipv4.ip_forward = 0net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0
Remove all daemons (and packages) not being used
This reduces attack footprint and improves performance
Many daemons listen on the network and could be accessible
rpm -qf /etc/rc.d/init.d/name rpm -e package-nameOR
chkconfig <service> offNotes
Leave cpuspeed for speedshifting cpu and irqbalance for multicore
Disable readahead, mcstransd, firstboot, (and NetworkManager for machines without wireless networking) since they are not needed.
#!/bin/sh /usr/sbin/ntpdate ntp-server
Only allow root and people with verified need to run cron jobs
Setup cron.allow and cron.deny
Setup equivalents if you have 'at' installed
Hide Apache Information
You should hide apache banner information from being displayed so the attackers are not aware of what version of Apache version you are running and thus making it more difficult for them to exploit any system holes and thus making vulnerability scanners work harder and in some cases impossible without knowing banner information.
Change the ServerSignature line to: ServerSignature Off
Change the ServerTokens line to: ServerTokens Prod
Restart Apache: /sbin/service httpd restart
A "SYN Attack" is a denial of service attack that consumes all the resources on a machine. Any server that is connected to a network is potentially subject to this attack.
Disable IP Source Routing
Source Routing is used to specify a path or route through the network from source to destination. This feature can be used by network people for diagnosing problems. However, if an intruder was able to send a source routed packet into the network, then he could intercept the replies and your server might not know that it's not communicating with a trusted server.
To enable Source Route Verification, edit the /etc/sysctl.conf file and add the following line:
net.ipv4.conf.all.accept_source_route = 0
To enable TCP SYN Cookie Protection, edit the /etc/sysctl.conf file and add the following line:
net.ipv4.tcp_syncookies = 1Disable ICMP Redirect Acceptance
ICMP redirects are used by routers to tell the server that there is a better path to other networks than the one chosen by the server. However, an intruder could potentially use ICMP redirect packets to alter the hosts's routing table by causing traffic to use a path you didn't intend.
To disable ICMP Redirect Acceptance, edit the /etc/sysctl.conf file and add the following line:
net.ipv4.conf.all.accept_redirects = 0Enable IP Spoofing Protection
IP spoofing is a technique where an intruder sends out packets which claim to be from another host by manipulating the source address. IP spoofing is very often used for denial of service attacks. For more information on IP Spoofing, I recommend the article IP Spoofing: Understanding the basics.
To enable IP Spoofing Protection, turn on Source Address Verification. Edit the /etc/sysctl.conf file and add the following line:
net.ipv4.conf.all.rp_filter = 1Enable Ignoring to ICMP Requests
If you want or need Linux to ignore ping requests, edit the /etc/sysctl.conf file and add the following line:
net.ipv4.icmp_echo_ignore_all = 1This cannot be done in many environments.
Enable Ignoring Broadcasts Request
If you want or need Linux to ignore broadcast requests, edit the /etc/sysctl.conf file and add the following line:
net.ipv4.icmp_echo_ignore_broadcasts = 1Enable Bad Error Message Protection
To alert you about bad error messages in the network, edit the /etc/sysctl.conf file and add the following line:
net.ipv4.icmp_ignore_bogus_error_responses = 1Enable Logging of Spoofed Packets, Source Routed Packets, Redirect Packets
To turn on logging for Spoofed Packets, Source Routed Packets, and Redirect Packets, edit the /etc/sysctl.conf file and add the following line:
net.ipv4.conf.all.log_martians = 1
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Last updated: March 12, 2019