| Dmitry Teselkin | af730f9 | 2018-08-16 11:29:55 +0300 | [diff] [blame] | 1 | # 3.2.5 Ensure broadcast ICMP requests are ignored |
| 2 | # |
| 3 | # Description |
| 4 | # =========== |
| 5 | # Setting net.ipv4.icmp_echo_ignore_broadcasts to 1 will cause the |
| 6 | # system to ignore all ICMP echo and timestamp requests to broadcast |
| 7 | # and multicast addresses. |
| 8 | # |
| 9 | # Rationale |
| 10 | # ========= |
| 11 | # Accepting ICMP echo and timestamp requests with broadcast or multicast |
| 12 | # destinations for your network could be used to trick your host into starting |
| 13 | # (or participating) in a Smurf attack. A Smurf attack relies on an attacker |
| 14 | # sending large amounts of ICMP broadcast messages with a spoofed source |
| 15 | # address. All hosts receiving this message and responding would send |
| 16 | # echo-reply messages back to the spoofed address, which is probably not |
| 17 | # routable. If many hosts respond to the packets, the amount of traffic on |
| 18 | # the network could be significantly multiplied. |
| 19 | # |
| 20 | # Audit |
| 21 | # ===== |
| 22 | # |
| 23 | # Run the following commands and verify output matches: |
| 24 | # |
| 25 | # # sysctl net.ipv4.icmp_echo_ignore_broadcasts |
| 26 | # net.ipv4.icmp_echo_ignore_broadcasts = 1 |
| 27 | # |
| 28 | # Remediation |
| 29 | # =========== |
| 30 | # |
| 31 | # Set the following parameter in the /etc/sysctl.conf file: |
| 32 | # |
| 33 | # net.ipv4.icmp_echo_ignore_broadcasts = 1 |
| 34 | # |
| 35 | # Run the following commands to set the active kernel parameters: |
| 36 | # |
| 37 | # # sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1 |
| 38 | # # sysctl -w net.ipv4.route.flush=1 |
| 39 | |
| 40 | parameters: |
| 41 | linux: |
| 42 | system: |
| 43 | kernel: |
| 44 | sysctl: |
| 45 | net.ipv4.icmp_echo_ignore_broadcasts: 1 |