18.4.5 (L1) Ensure 'MSS: (EnableICMPRedirect) Allow ICMP redirects to override OSPF generated routes' is set to 'Disabled'


Internet Control Message Protocol (ICMP) redirects cause the IPv4 stack to plumb host routes. These routes override the Open Shortest Path First (OSPF) generated routes.
The recommended state for this setting is: Disabled.

This behavior is expected. The problem is that the 10 minute time-out period for the ICMP redirect-plumbed routes temporarily creates a network situation in which traffic will no longer be routed properly for the affected host. Ignoring such ICMP redirects will limit the system's exposure to attacks that will impact its ability to participate on the network.


To establish the recommended configuration via GP, set the following UI path to Disabled:
Computer Configuration\Policies\Administrative Templates\MSS (Legacy)\MSS: (EnableICMPRedirect) Allow ICMP redirects to override OSPF generated routes
Note: This Group Policy path does not exist by default. An additional Group Policy template (MSS-legacy.admx/adml) is required - it is available from this TechNet blog post: The MSS settings ? Microsoft Security Guidance blog

When Routing and Remote Access Service (RRAS) is configured as an autonomous system boundary router (ASBR), it does not correctly import connected interface subnet routes. Instead, this router injects host routes into the OSPF routes. However, the OSPF router cannot be used as an ASBR router, and when connected interface subnet routes are imported into OSPF the result is confusing routing tables with strange routing paths.

Default Value:
Enabled. (ICMP redirects can override OSPF-generated routes.)

1. CCE-34597-5

See Also


Item Details


References: 800-53|SI-4, CSCv6|9, CSCv7|9.2, CSCv7|9.3

Plugin: Windows

Control ID: 103fc6d7d27c4de39994db490b488ddc2b6bd2a76ef2b196204f78ebc43b48aa