Mastering Linux Security and Hardening - Second Edition

Blocking ICMP with iptables

The conventional wisdom that you may have heard for most of your career is that we need to block all the packets from the Internet Control Message Protocol (ICMP). The idea you may have been told is to make your server invisible to hackers by blocking ping packets. Of course, there are some vulnerabilities that are associated with ICMP, such as the following:

• By using a botnet, a hacker could inundate your server with ping packets from multiple sources at once, exhausting your server's ability to cope. 
• Certain vulnerabilities that are associated with the ICMP protocol can allow a hacker to either gain administrative privileges on your system, redirect your traffic to a malicious server, or crash your operating ...