The SUSE operating system must prevent Internet Protocol version 6 (IPv6) Internet Control Message Protocol (ICMP) redirect messages from being accepted.

STIG ID: SLES-12-030363  |  SRG: SRG-OS-000480-GPOS-00227 |  Severity: medium |  CCI: CCI-000366 |  Vulnerability Id: V-237621

Vulnerability Discussion

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.

Check

Verify the SUSE operating system does not accept IPv6 source-routed packets by default.
Verify the SUSE operating system does not accept IPv6 ICMP redirect messages.

Check the value of the IPv6 accept_redirects variable with the following command:

> sudo sysctl net.ipv6.conf.all.accept_redirects
net.ipv6.conf.all.accept_redirects =0

If the network parameter "ipv6.conf.all.accept_redirects" is not equal to "0" or nothing is returned, this is a finding.

Fix

Configure the SUSE operating system to not accept IPv6 ICMP redirect messages by running the following command as an administrator:

> sudo sysctl -w net.ipv6.conf.all.accept_redirects=0

If "0" is not the system's default value, add or update the following line in "/etc/sysctl.d/99-stig.conf":

> sudo sh -c 'echo "net.ipv6.conf.all.accept_redirects=0" >> /etc/sysctl.d/99-stig.conf'

> sudo sysctl --system
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