Plain Text Options for outbound email must be configured.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-17761	DTOO228 - Outlook	SV-33505r2_rule	ECSC-1	Medium

Description
If outgoing mail is formatted in certain ways, for example if attachments are encoded in UUENCODE format, attackers might manipulate the messages for their own purposes. If UUENCODE formatting is used, an attacker could manipulate the encoded attachment to bypass content filtering software. Outlook 2010 automatically wraps plain text messages and uses the standard MIME format to encode attachments in plain text messages. However, these settings can be altered to allow e-mail to be read in plain text e-mail programs that use a non-standard line length or that cannot process MIME attachments.

Description

If outgoing mail is formatted in certain ways, for example if attachments are encoded in UUENCODE format, attackers might manipulate the messages for their own purposes. If UUENCODE formatting is used, an attacker could manipulate the encoded attachment to bypass content filtering software. Outlook 2010 automatically wraps plain text messages and uses the standard MIME format to encode attachments in plain text messages. However, these settings can be altered to allow e-mail to be read in plain text e-mail programs that use a non-standard line length or that cannot process MIME attachments.

STIG	Date
Microsoft Outlook 2010	2014-01-07

Details

Check Text ( C-33991r3_chk )
The policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2010 -> Outlook Options -> Mail format -> Internet Formatting "Plain text options" must be set to "Enabled" where line length is "132" and that NO Check is visible in the "Encode all attachments in UUENCODE format when sending a plain text message" checkbox option. Procedure: Use the Windows Registry Editor to navigate to the following key: HKCU\Software\Policies\Microsoft\Office\14.0\common\mailsettings Criteria: If the value PlainWrapLen is REG_DWORD = 132 (decimal), this is not a finding. AND HKCU\Software\Policies\Microsoft\Office\14.0\outlook\options\mail Criteria: If the value Message Plain Format Mime is REG_DWORD = 1, this is not a finding.

Check Text ( C-33991r3_chk )

The policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2010 -> Outlook Options -> Mail format -> Internet Formatting "Plain text options" must be set to "Enabled" where line length is "132" and that NO Check is visible in the "Encode all attachments in UUENCODE format when sending a plain text message" checkbox option.

Procedure: Use the Windows Registry Editor to navigate to the following key:

HKCU\Software\Policies\Microsoft\Office\14.0\common\mailsettings

Criteria: If the value PlainWrapLen is REG_DWORD = 132 (decimal), this is not a finding.

AND

HKCU\Software\Policies\Microsoft\Office\14.0\outlook\options\mail

Criteria: If the value Message Plain Format Mime is REG_DWORD = 1, this is not a finding.

Fix Text (F-29680r1_fix)
Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2010 -> Outlook Options -> Mail format -> Internet Formatting "Plain text -> options" to "Enabled" where line length is "132" and that NO Check is visible in the "Encode all attachments in UUENCODE format when sending a plain text message" checkbox option.