Details

Outlook uses two levels of security to restrict access to files attached to email messages or other items. Files with specific extensions can be categorized as Level 1 (users cannot view the file) or Level 2 (users can open the file after saving it to disk). Users can freely open files of types that are not categorized as Level 1 or Level 2. If users can demote Level 1 files to Level 2, they will be able to access potentially dangerous files after saving them to disk, which could allow malicious code to affect their computers or compromise the security of sensitive information.

Solution

Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Security Form Settings -> Attachment Security ‘Allow users to demote attachments to Level 2’ to ‘Disabled’.

Supportive Information

The following resource is also helpful.

• https://iasecontent.disa.mil/stigs/zip/U_MS_Outlook_2013_V1R13_STIG.zip

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

References

• 800-53|SC-18(1)
• CAT|II
• CCI|CCI-001662
• Rule-ID|SV-53954r1_rule
• STIG-ID|DTOO241
• Vuln-ID|V-17569

Source

• Tenable.com/audits