Title

The system must limit how many times unacknowledged TCP data is retransmitted. (Cat III impact)

Discussion

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.

Check Content

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

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.)

Additional Identifiers

Rule ID: SV-225489r852258_rule

Vulnerability ID: V-225489

Group Title: SRG-OS-000420-GPOS-00186

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.