Evil PGP sigs thread must die. was Re: Stop it with putting your e-mail body in my MUA OT

Thu Jul 11 00:36:07 UTC 2002

On 01:30 PM 7/10/02, Stephen Sprunk wrote:
 >
 >Thus spake "Andy Dills" <andy at xecu.net>
 >> Yes, but once again you must consider content, given that most mail
 >> clients don't automatically verify signatures. Most of us will have to
 >> make a judgement call as to whether or not to bother to check the
 >> signature.
 >>
 >> The higher the degree of "importance" of the content, the more likely I am
 >> to check the signature, and the more likely I am to take verification
 >> steps if not signed.
 >>
 >> If the content is not "important", I won't bother checking the signature.
 >
 >Why not just upgrade to a modern MUA and not have to worry?
 >
 >OE only supports S/MIME for now, but it does automatically verify every 
message,
 >including checking that the From: line matches the key.  It makes a big 
stink if
 >the signature doesn't match, but just displays a simple little icon if it's
 >verified correctly.  How can you prefer to check messages manually and 
therefore
 >cause the problems you describe?

Maybe the following has something to do with his desire to avoid using 
Micro$oft products as you advocate, *especially* as regards to letting a M$ 
email client automatically process PGP .sigs on incoming email.

jc  "the timing couldn't have been better" dill

<http://www.eeye.com/html/Research/Advisories/AD20020710.html>

Remote PGP Outlook Encryption Plug-in Vulnerability

Release Date:
July 10, 2002

Severity:
High (Remote Code Execution)

Systems Affected:
NAI PGP Desktop Security 7.0.4
NAI PGP Personal Security 7.0.3
NAI PGP Freeware 7.0.3

Description:

The beer is still cold, the days are still long, the exploits still start as
jokes (this time over a beer with a three letter agency) and the
advisories... we'll just say, "All of your SCADA are belong to us."

A vulnerability in the NAI PGP Outlook plug-in can be exploited to remotely
execute code on any system that uses the NAI PGP Outlook plug-in's. By
sending a carefully crafted email the message decoding functionality can be
manipulated to overwrite various heap structures pertinent to the PGP
plug-in.

This vulnerability can be exploited by a user simply selecting a "malicious"
email, the opening of attachments is not required. When the attack is
performed against a target system, malicious code will be executed within
the context of the user receiving the email. This can lead to the compromise
of the targets machine, as well as their PGP encrypted communications. It
should also be noted that because of the nature of the SMTP protocol this
vulnerability can be exploited anonymously.

Technical Description:

Exploitation:

By creating a malformed email we can overwrite a section of heap memory that
contains various data. By overwriting this section of heap with valid
addresses of an unused section in the PEB, which is the same across all NT
systems, we can walk the email parsing and eventually get to something
easily exploitable:

CALL DWORD PTR [ecx]

This pointer addresses references a function pointer list. At the time of
exploitation, an attacker controlled buffer address is the first item on the
stack. By overwriting the function pointer list pointer address with the
address of an Import table, we can call any imported function. Our current
stack will be passed into the function for parameter use. as is. The first
item on our stack is an address that points to attacker-controlled data.

By overwriting the address, with the address of the
SetUnhandledExceptionFilter() IAT entry, execution will redirect into this
address when the default exception handler is called,

After returning from SetUnhandledExceptionFilter() PGP Outlook will fail as
it crawls back down the call stack, after cycling through the exception list
it will call the DefaultExceptionFilter, which now contains the address of
our code. This of course can also be exploited silently using frame
reconstruction.

Due to the large size of an example vulnerable email we are not including it
in our advisory. We will be updating the research section of our website
with a link to an example email. http://www.eEye.com

Where do you want your secret key to go today?

Vendor Status: NAI has worked quickly to safeguard customers against this
vulnerability. They have released a patch, for the latest versions of the
PGP Outlook plug-in, to protect systems from this flaw. You may download the
patch from:
http://www.nai.com/naicommon/download/upgrade/patches/patch-pgphotfix.asp
Note: This issue does not affect PGP Corporate Desktop users.

Discover: Marc Maiffret
Exploitation: Riley Hassell

Greetings: Kasia, and the hot photographer from Inc Magazine. Phil
Zimmerman, the godfather of personal privacy, much respect.

Copyright (c) 1998-2002 eEye Digital Security
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