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The system must ignore ICMPv6 redirects by default.


Finding ID Version Rule ID IA Controls Severity
V-217926 RHEL-06-000099 SV-217926r505923_rule Medium
An illicit ICMP redirect message could result in a man-in-the-middle attack.
Red Hat Enterprise Linux 6 Security Technical Implementation Guide 2020-09-03


Check Text ( C-19407r376793_chk )
If IPv6 is disabled, this is not applicable.

The status of the "net.ipv6.conf.default.accept_redirects" kernel parameter can be queried by running the following command:

$ sysctl net.ipv6.conf.default.accept_redirects
net.ipv6.conf.default.accept_redirects = 0

$ grep net.ipv6.conf.default.accept_redirects /etc/sysctl.conf /etc/sysctl.d/*
net.ipv6.conf.default.accept_redirects = 0

If "net.ipv6.conf.default.accept_redirects" is not configured in the /etc/sysctl.conf file or in the /etc/sysctl.d/ directory, is commented out or does not have a value of "0", this is a finding.
Fix Text (F-19405r376794_fix)
To set the runtime status of the "net.ipv6.conf.default.accept_redirects" kernel parameter, run the following command:

# sysctl -w net.ipv6.conf.default.accept_redirects=0

Set the system to the required kernel parameter by adding the following line to "/etc/sysctl.conf" or a config file in the /etc/sysctl.d/ directory (or modify the line to have the required value):

net.ipv6.conf.default.accept_redirects = 0

Issue the following command to make the changes take effect:

# sysctl --system