The system must limit how many times unacknowledged TCP data is retransmitted.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-4438	WN12-SO-000048	SV-52929r1_rule	ECSC-1	Low

Description
In a SYN flood attack, the attacker sends a continuous stream of SYN packets to a server, and the server leaves the half-open connections open until it is overwhelmed and is no longer able to respond to legitimate requests.

STIG	Date
Windows Server 2012 / 2012 R2 Domain Controller Security Technical Implementation Guide	2014-06-30

Details

Check Text ( C-47234r2_chk )
If the following registry value does not exist or is not configured as specified, this is a finding: Registry Hive: HKEY_LOCAL_MACHINE Registry Path: \System\CurrentControlSet\Services\Tcpip\Parameters\ Value Name: TcpMaxDataRetransmissions Value Type: REG_DWORD Value: 3 (or less)

Fix Text (F-45855r2_fix)
Configure the policy value for Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options -> "MSS: (TcpMaxDataRetransmissions) How many times unacknowledged data is retransmitted (3 recommended, 5 is the default)" to "3" or less. (See "Updating the Windows Security Options File" in the STIG Overview document if MSS settings are not visible in the system's policy tools.)

Fix Text (F-45855r2_fix)

Configure the policy value for Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options -> "MSS: (TcpMaxDataRetransmissions) How many times unacknowledged data is retransmitted (3 recommended, 5 is the default)" to "3" or less.

(See "Updating the Windows Security Options File" in the STIG Overview document if MSS settings are not visible in the system's policy tools.)