Details

Spam originators, in an effort to refine mailing lists, sometimes monitor transmissions for automated bounce-back messages. Automated messages include such items as ‘Out of Office’ responses, nondelivery messages, or automated message forwarding.

Automated bounce-back messages can be used by a third party to determine if users exist on the server. This can result in the disclosure of active user accounts to third parties, paving the way for possible future attacks.

Solution

Open the Exchange Management Shell and enter the following command:

Set-RemoteDomain -Identity <'IdentityName'> -AllowedOOFType ‘InternalLegacy’

Note: The and InternalLegacy values must be in quotes.

Supportive Information

The following resource is also helpful.

• https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_MS_Exchange_2013_Y21M01_STIG.zip

This security hardening control applies to the following category of controls within NIST 800-53: System and Information Integrity.This control applies to the following type of system Windows.

References

• 800-53|SI-8(2)
• CAT|II
• CCI|CCI-001308
• Rule-ID|SV-207314r615936_rule
• STIG-ID|EX13-MB-000240
• STIG-Legacy|SV-84657
• STIG-Legacy|V-70035
• Vuln-ID|V-207314

Source

• Tenable.com/audits