The Exchange Simple Mail Transfer Protocol (SMTP) IP Allow List Connection filter must be enabled.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-259624	EX19-ED-000138	SV-259624r961161_rule		Medium

Description
Email system availability depends in part on best practice strategies for setting tuning configurations. Careful tuning reduces the risk that system or network congestion will contribute to availability impacts. Filters that govern inbound email evaluation can significantly reduce spam, phishing, and spoofed emails. Filters for messages from blank senders, known spammers, or zero-day attack modifications must be enabled to be effective. Having items identified in the Allow List causes other spam evaluation steps to be bypassed and therefore should be used only with an abundance of caution. If spammers were to learn of entries in the Allow List, it could enable them to plan a denial of service attack (or other attack) by spoofing that source.

Description

Email system availability depends in part on best practice strategies for setting tuning configurations. Careful tuning reduces the risk that system or network congestion will contribute to availability impacts. Filters that govern inbound email evaluation can significantly reduce spam, phishing, and spoofed emails. Filters for messages from blank senders, known spammers, or zero-day attack modifications must be enabled to be effective. Having items identified in the Allow List causes other spam evaluation steps to be bypassed and therefore should be used only with an abundance of caution. If spammers were to learn of entries in the Allow List, it could enable them to plan a denial of service attack (or other attack) by spoofing that source.

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

Details

Check Text ( C-63363r942184_chk )
Open the Exchange Management Shell and enter the following command: Get-IPAllowListConfig \| Select-Object -Property Name, Enabled If the value for "Enabled" is not set to "True", this is a finding. Note: "Enabled" set to "True" is the default value.

Fix Text (F-63271r942185_fix)
Open the Exchange Management Shell and enter the following command: Set-IPAllowListConfig -Enabled $true