Software Engineering Institute

Transport Neutral Encapsulation Format (TNEF)

TNEF is a proprietary Microsoft format for encoding rich text email messages. Microsoft Outlook and Microsoft Exchange support the use of TNEF-encoded messages.

The problem

Microsoft Outlook and Microsoft Exchange do not properly validate TNEF MIME attachments, potentially allowing a buffer overflow to occur. The overflow occurs in in the process that decodes TNEF MIME attachments. A remote attacker may be able trigger the buffer overflow by sending a specially crafted TNEF MIME attachment to a vulnerable Outlook or Exchange installation.

Note that on user workstations, exploitation may require a user to open or preview a malicious mail message in Outlook. However, on Exchange servers, this vulnerability can be exploited without human interaction.

For more information, please see Microsoft Security Bulletin MS06-003.

A remote unauthenticated attacker may be able to execute arbitrary code on a system running the vulnerable software. Microsoft Outlook can trigger the vulnerability when it opens or displays a preview for a specially crafted message. Microsoft Exchange can trigger the vulnerability when it processes a specially crafted message.

Apply a patch from your vendor
Microsoft addresses this vulnerability with the updates listed in Microsoft Security Bulletin MS06-003.

Workarounds

Microsoft has listed several workarounds in Microsoft Security Bulletin MS06-003, including blocking attachments with the MIME type of application/ms-tnef.