Exchange Message size restrictions must be controlled on Receive connectors.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-70009	EX13-MB-000175	SV-84631r1_rule		Low

Description
Email system availability depends in part on best practice strategies for setting tuning configurations. For message size restrictions, multiple places exist to set or override inbound or outbound message size. Failure to control the configuration strategy can result in loss of data or system availability. This setting enables the administrator to control the maximum message size on receive connectors. Using connectors to control size limits may necessitate applying message size limitations in multiple places, with the potential of introducing conflicts and impediments in the mail flow. Changing this setting at the connector overrides the global one. Therefore, if operational needs require it, the connector value may be set lower than that of the global value with the rationale documented in the Email Domain Security Plan (EDSP).

Description

Email system availability depends in part on best practice strategies for setting tuning configurations. For message size restrictions, multiple places exist to set or override inbound or outbound message size. Failure to control the configuration strategy can result in loss of data or system availability. This setting enables the administrator to control the maximum message size on receive connectors. Using connectors to control size limits may necessitate applying message size limitations in multiple places, with the potential of introducing conflicts and impediments in the mail flow. Changing this setting at the connector overrides the global one. Therefore, if operational needs require it, the connector value may be set lower than that of the global value with the rationale documented in the Email Domain Security Plan (EDSP).

STIG	Date
MS Exchange 2013 Mailbox Server Security Technical Implementation Guide	2017-04-06

Details

Check Text ( C-70483r1_chk )
Review the Email Domain Security Plan (EDSP). Determine the global maximum message receive size and whether signoff with risk acceptance is documented for the Receive connector to have a different value. Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector \| Select Name, Identity, MaxMessageSize Identify Internet-facing connectors. For each Receive connector, if the value of MaxMessageSize is not the same as the global value, this is a finding. or If MaxMessageSize is set to a numeric value different from the global value and has signoff and risk acceptance in the EDSP, this is not a finding.

Check Text ( C-70483r1_chk )

Review the Email Domain Security Plan (EDSP).

Determine the global maximum message receive size and whether signoff with risk acceptance is documented for the Receive connector to have a different value.

Open the Exchange Management Shell and enter the following command:

Get-ReceiveConnector | Select Name, Identity, MaxMessageSize

Identify Internet-facing connectors.

For each Receive connector, if the value of MaxMessageSize is not the same as the global value, this is a finding.

or

If MaxMessageSize is set to a numeric value different from the global value and has signoff and risk acceptance in the EDSP, this is not a finding.

Fix Text (F-76245r1_fix)
Update the EDSP. Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -MaxMessageSize <'MaxReceiveSize'> Note: The and values must be in quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance. Repeat the procedure for each Receive connector.