Detections
Analytics

2.1.9 Ensure that DKIM is enabled for all Exchange Online Domains

Information

DKIM is one of the trio of Authentication methods (SPF, DKIM and DMARC) that help prevent attackers from sending messages that look like they come from your domain.

DKIM lets an organization add a digital signature to outbound email messages in the message header. When DKIM is configured, the organization authorizes it's domain to associate, or sign, it's name to an email message using cryptographic authentication. Email systems that get email from this domain can use a digital signature to help verify whether incoming email is legitimate.

Use of DKIM in addition to SPF and DMARC to help prevent malicious actors using spoofing techniques from sending messages that look like they are coming from your domain.

By enabling DKIM with Office 365, messages that are sent from Exchange Online will be cryptographically signed. This will allow the receiving email system to validate that the messages were generated by a server that the organization authorized and not being spoofed.

NOTE: Nessus has provided the target output to assist in reviewing the benchmark to ensure target compliance.

Solution

To remediate using the UI:

 - Navigate to Microsoft Defender https://security.microsoft.com/
 - Expand Email & collaboration > Policies & rules > Threat policies.
 - Under Rules section click Email authentication settings.
 - Select DKIM
 - Select the domain to remediate.
 - Click Create DKIM keys.
 - Microsoft provides the properly formatted CNAME records, copy these for later use.
 - In another browser tab or window, go to the domain registrar for the domain, and then create the two CNAME records using the information from the previous step.
 - Return the domain properties flyout and toggle Sign messages for this domain with DKIM signatures to Enabled.

If successful the status will show Signing DKIM signatures for this domain.

Impact:

There should be no impact of setting up DKIM however, organizations should ensure appropriate setup to ensure continuous mail-flow.

See Also

https://workbench.cisecurity.org/benchmarks/24620

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-7, CSCv7|7.8

Plugin: microsoft_azure

Control ID: fd6ce2600dd9b402aae4fdad7b2550e9c4c0792869723a4cbe3d2471d91e9ad2