Exchange internal Send connectors must require encryption.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-259642	EX19-ED-000236	SV-259642r961632_rule		High

Description
The Simple Mail Transfer Protocol (SMTP) connector is used by Exchange to send and receive messages from server to server. Several controls work together to provide security between internal servers. This setting controls the encryption method used for communications between servers. With this feature enabled, only servers capable of supporting Transport Layer Security (TLS) will be able to send and receive mail within the domain. The use of secure communication prevents eavesdroppers from reading or modifying communications between mail clients and servers. While sensitive message bodies should be encrypted by the sender at the client, requiring a secure connection from server to server adds protection by encrypting the sender and recipient information that cannot be encrypted by the sender. Individually, channel security and encryption can be compromised by attackers. Used together, email becomes a more difficult target, and security is heightened. Failure to enable this feature gives eavesdroppers an opportunity to read or modify messages between servers.

Description

The Simple Mail Transfer Protocol (SMTP) connector is used by Exchange to send and receive messages from server to server. Several controls work together to provide security between internal servers. This setting controls the encryption method used for communications between servers. With this feature enabled, only servers capable of supporting Transport Layer Security (TLS) will be able to send and receive mail within the domain. The use of secure communication prevents eavesdroppers from reading or modifying communications between mail clients and servers. While sensitive message bodies should be encrypted by the sender at the client, requiring a secure connection from server to server adds protection by encrypting the sender and recipient information that cannot be encrypted by the sender. Individually, channel security and encryption can be compromised by attackers. Used together, email becomes a more difficult target, and security is heightened. Failure to enable this feature gives eavesdroppers an opportunity to read or modify messages between servers.

STIG	Date
Microsoft Exchange 2019 Edge Server Security Technical Implementation Guide	2024-06-10

Details

Check Text ( C-63381r942238_chk )
Check the Email Domain Security Plan (EDSP) and determine which send connector is using which secure validation method. If no configuration setting is found, this is a finding. If using "DomainValidation", open the Exchange Management Shell and enter the following command: Get-SendConnector \| Select-Object -Property Name, Identity, TlsDomain If the value of "TlsDomain" is not set to the value of the internal <'SMTP Domain'>, this is a finding. If using "DomainSecureEnabled", open the Exchange Management Shell and enter the following command: Get-SendConnector \| Select-Object -Property Name, Identity, DomainSecureEnabled If the value of 'DomainSecureEnabled' is not set to 'True', this is a finding. Note: The wildcard character (*) is not supported in domains that are configured for mutual TLS authentication. The same domain must also be defined on the corresponding Receive connector and in the TLSReceiveDomainSecureList attribute of the transport configuration.

Check Text ( C-63381r942238_chk )

Check the Email Domain Security Plan (EDSP) and determine which send connector is using which secure validation method. If no configuration setting is found, this is a finding.

If using "DomainValidation", open the Exchange Management Shell and enter the following command:

Get-SendConnector | Select-Object -Property Name, Identity, TlsDomain

If the value of "TlsDomain" is not set to the value of the internal <'SMTP Domain'>, this is a finding.

If using "DomainSecureEnabled", open the Exchange Management Shell and enter the following command:

Get-SendConnector | Select-Object -Property Name, Identity, DomainSecureEnabled

If the value of 'DomainSecureEnabled' is not set to 'True', this is a finding.

Note: The wildcard character (*) is not supported in domains that are configured for mutual TLS authentication. The same domain must also be defined on the corresponding Receive connector and in the TLSReceiveDomainSecureList attribute of the transport configuration.

Fix Text (F-63289r942239_fix)
If using "DomainValidation", open the Exchange Management Shell and enter the following command: Set-SendConnector -Identity <'Identity'> -TlsDomain -TlsAuthLevel DomainValidation -RequireTLS $true If using "DomainSecureEnabled", open the Exchange Management Shell and enter the following command: Set-SendConnector -Identity <'ReceiveConnector'> -DomainSecureEnabled $true Note: - To use DomainSecureEnabled, DNSRouting must be set to $true. - The same domain must also be defined on the corresponding Receive connector and in the TLSReceiveDomainSecureList attribute of the transport configuration.

Fix Text (F-63289r942239_fix)

If using "DomainValidation", open the Exchange Management Shell and enter the following command:

Set-SendConnector -Identity <'Identity'> -TlsDomain -TlsAuthLevel DomainValidation -RequireTLS $true

If using "DomainSecureEnabled", open the Exchange Management Shell and enter the following command:

Set-SendConnector -Identity <'ReceiveConnector'> -DomainSecureEnabled $true

Note:
- To use DomainSecureEnabled, DNSRouting must be set to $true.
- The same domain must also be defined on the corresponding Receive connector and in the TLSReceiveDomainSecureList attribute of the transport configuration.