Outlook makes 99% CPU Usage with this message

From: Kayne Ian (Softlab) (Ian.Kayne@softlab.co.uk)
Date: 08/29/01 

Message-ID: <CDD7435C5120D511870B00805F6FED1D5410F6@birexm01.uk.softlab.net>
From: "Kayne Ian (Softlab)" <Ian.Kayne@softlab.co.uk>
To: Vuln-Dev <VULN-DEV@SECURITYFOCUS.COM>
Subject: Outlook makes 99% CPU Usage with this message
Date: Wed, 29 Aug 2001 16:18:31 +0100

Hey all,
        This is a strange one. I've been hashing this about for a while, and
come up with the following. In the attached zip is a message saved out in
Outlook normal message format. You can open, read, close, forward etc this
message absolutely fine. But when you try and click reply, it immediately
sends Outlook to 100% CPU usage, and it doesn't come back. I have no idea
why, but it seems to be outlook getting confused with the message body - if
you hex the .msg file you'll see 2 lines of asterixes that are not displayed
(and no, it's not cause they are white text on white background, you should
still be able to highlight them, but they just arent there).

        Now, this crashes my Outlook every time. Thats Outlook 2k
v9.0.0.3821 running on Win2k Pro. It's crashed a few other ppls outlooks,
but strangely on some Outlooks (same version as mine) it has no effect. I'm
wondering if it's to do with a certain combination of patches etc installed.

        So, 2 things for you guys. Firstly, do the following:

1. Exit outlook
2. Unzip the .msg file from the zip
3. Load outlook
4. Double click the .msg file from explorer or somwhere
5. Click the Reply button

It should crash Outlook immediately. The Exit/Load outlook thing is
important.

        Secondly, if that doesn't crash, see if you can see 2 rows of *'s
around the disclaimer. If you save the message as rtf or plain text, or hex
dump the .msg the asterixes are there. But not when you view the message in
Outlook. I have no idea of the format of a .msg file, so maybe someone else
with more experience with this stuff can help?

        Anyway, I can't garantee it will work, and that it's not just my
machines being screwy. But if it does work, and maybe if it's exploitable,
it's pretty damn nasty. An invisible exploit in a plain message with no
attachment that only needs a click on Reply to work? Ouch.

Ian Kayne
Technical Specialist - IT Solutions
Softlab Ltd - A BMW Company

 <<Test.zip>>

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