Title

Warning about invalid signatures must be enforced. (Cat II impact)

Discussion

If users open email messages that include invalid digital signatures, Outlook displays a warning dialog box. Users can decide whether they want to be warned about invalid signatures in the future. If users are not notified about invalid signatures, they might be prevented from detecting a fraudulent signature sent by a malicious person.

Check Content

Verify the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Cryptography "Signature Warning" is "Enabled (Always warn about invalid signatures)". Procedure: Use the Windows Registry Editor to navigate to the following key: HKCU\Software\Policies\Microsoft\Office\15.0\outlook\security Criteria: If the value WarnAboutInvalid is REG_DWORD = 1, this is not a finding.

Fix Text

Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2013 -> Security -> Cryptography "Signature Warning" to "Enabled (Always warn about invalid signatures)".

Additional Identifiers

Rule ID: SV-54024r1_rule

Vulnerability ID: V-17803

Group Title: DTOO265 - Signature Warnings

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.