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18.5.5 (L2) Ensure 'MSS: (KeepAliveTime) How often keep-alive packets are sent in milliseconds' is set to 'Enabled: 300,000 or 5 minutes'

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Information

This value controls how often TCP attempts to verify that an idle connection is still intact by sending a keep-alive packet. If the remote computer is still reachable, it acknowledges the keep-alive packet.

The recommended state for this setting is: Enabled: 300,000 or 5 minutes.

An attacker who is able to connect to network applications could establish numerous connections to cause a DoS condition.

Solution

To establish the recommended configuration via GP, set the following UI path to Enabled: 300,000 or 5 minutes :

Computer Configuration\Policies\Administrative Templates\MSS (Legacy)\MSS: (KeepAliveTime) How often keep-alive packets are sent in milliseconds

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 https://blogs.technet.microsoft.com/secguide/2016/10/02/the-mss-settings/

Impact:

Keep-alive packets are not sent by default by Windows. However, some applications may configure the TCP stack flag that requests keep-alive packets. For such configurations, you can lower this value from the default setting of two hours to five minutes to disconnect inactive sessions more quickly.

See Also

https://workbench.cisecurity.org/benchmarks/24135

Item Details

Category: CONFIGURATION MANAGEMENT, SYSTEM AND SERVICES ACQUISITION

References: 800-53|CM-2, 800-53|CM-6, 800-53|CM-7, 800-53|CM-7(1), 800-53|CM-9, 800-53|SA-3, 800-53|SA-8, 800-53|SA-10

Plugin: Windows

Control ID: a23ddb8bcfbe1c65c978466de1d8b67c5dcb6a01a72e807edfbf1e3aebf2f599