| # 3.2.5 Ensure broadcast ICMP requests are ignored |
| # |
| # Description |
| # =========== |
| # Setting net.ipv4.icmp_echo_ignore_broadcasts to 1 will cause the |
| # system to ignore all ICMP echo and timestamp requests to broadcast |
| # and multicast addresses. |
| # |
| # Rationale |
| # ========= |
| # Accepting ICMP echo and timestamp requests with broadcast or multicast |
| # destinations for your network could be used to trick your host into starting |
| # (or participating) in a Smurf attack. A Smurf attack relies on an attacker |
| # sending large amounts of ICMP broadcast messages with a spoofed source |
| # address. All hosts receiving this message and responding would send |
| # echo-reply messages back to the spoofed address, which is probably not |
| # routable. If many hosts respond to the packets, the amount of traffic on |
| # the network could be significantly multiplied. |
| # |
| # Audit |
| # ===== |
| # |
| # Run the following commands and verify output matches: |
| # |
| # # sysctl net.ipv4.icmp_echo_ignore_broadcasts |
| # net.ipv4.icmp_echo_ignore_broadcasts = 1 |
| # |
| # Remediation |
| # =========== |
| # |
| # Set the following parameter in the /etc/sysctl.conf file: |
| # |
| # net.ipv4.icmp_echo_ignore_broadcasts = 1 |
| # |
| # Run the following commands to set the active kernel parameters: |
| # |
| # # sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1 |
| # # sysctl -w net.ipv4.route.flush=1 |
| |
| parameters: |
| linux: |
| system: |
| kernel: |
| sysctl: |
| net.ipv4.icmp_echo_ignore_broadcasts: 1 |