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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-52929r2_rule 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 Member Server Security Technical Implementation Guide 2018-10-30

Details

Check Text ( C-47234r3_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-45855r3_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 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.)