3.3.5 Ensure icmp redirects are not accepted

Information

ICMP redirect messages are packets that convey routing information and tell your host (acting as a router) to send packets via an alternate path. It is a way of allowing an outside routing device to update your system routing tables.

ICMP redirect messages are packets that convey routing information and tell your host (acting as a router) to send packets via an alternate path. It is a way of allowing an outside routing device to update your system routing tables. By setting net.ipv4.conf.all.accept_redirects net.ipv4.conf.default.accept_redirects net.ipv6.conf.all.accept_redirects and net.ipv6.conf.default.accept_redirects to 0 the system will not accept any ICMP redirect messages, and therefore, won't allow outsiders to update the system's routing tables.

Solution

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

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

Example:

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

Run the following command to set the active kernel parameters:

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

-IF- IPv6 is enabled on the system:

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

- net.ipv6.conf.all.accept_redirects = 0
- net.ipv6.conf.default.accept_redirects = 0

Example:

# printf '%s
' "net.ipv6.conf.all.accept_redirects = 0" "net.ipv6.conf.default.accept_redirects = 0" >> /etc/sysctl.d/60-netipv6_sysctl.conf

Run the following command to set the active kernel parameters:

# {
sysctl -w net.ipv6.conf.all.accept_redirects=0
sysctl -w net.ipv6.conf.default.accept_redirects=0
sysctl -w net.ipv6.route.flush=1
}

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

See Also

https://workbench.cisecurity.org/benchmarks/15023

Item Details

Category: CONFIGURATION MANAGEMENT

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

Plugin: Unix

Control ID: edc754f7cedce6720493ebab372eca40e7cb925b207f8ba8320c8f4017549cf2