IT Best Practices Tip: nist_V-38548
Severity: medium
Short Description
The system must ignore ICMPv6 redirects by default.
Long Description
An illicit ICMP redirect message could result in a man-in-the-middle attack.
How to Check Correct Configuration
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
The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf".
$ grep net.ipv6.conf.default.accept_redirects /etc/sysctl.conf
If the correct value is not returned, this is a finding.
How to 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
If this is not the system's default value, add the following line to "/etc/sysctl.conf":
net.ipv6.conf.default.accept_redirects = 0