3.3.2 Ensure packet redirect sending is disabled

Information

ICMP Redirects are used to send routing information to other hosts. As a host itself does not act as a router (in a host only configuration), there is no need to send redirects.

An attacker could use a compromised host to send invalid ICMP redirects to other router devices in an attempt to corrupt routing and have users access a system set up by the attacker as opposed to a valid system.

Solution

Set the following parameters in /etc/sysctl.conf or a file in /etc/sysctl.d/ ending inconf :

- net.ipv4.conf.all.send_redirects = 0
- net.ipv4.conf.default.send_redirects = 0

Example:

# printf '%s
' "net.ipv4.conf.all.send_redirects = 0" "net.ipv4.conf.default.send_redirects = 0" >> /etc/sysctl.d/60-netipv4_sysctl.conf

Run the following script to set the active kernel parameters:

#!/usr/bin/env bash

{
sysctl -w net.ipv4.conf.all.send_redirects=0
sysctl -w net.ipv4.conf.default.send_redirects=0
sysctl -w net.ipv4.route.flush=1
}

Note: If these settings appear in a canonically later file, or later in the same file, these settings will be overwritten

Impact:

IP forwarding is required on systems configured to act as a router. If these parameters are disabled, the system will not be able to perform as a router.

See Also

https://workbench.cisecurity.org/benchmarks/18960

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6, 800-53|CM-7, CSCv7|9.2

Plugin: Unix

Control ID: ca81413bc3099fa6390f858aebf78d1625f976cec4764fed726511aaf28508d9