EEYE: Macromedia Shockwave Flash Malformed Header Overflow

From: Marc Maiffret (
Date: 08/09/02

From: "Marc Maiffret" <>
Date: Thu, 8 Aug 2002 17:26:20 -0700

Macromedia Shockwave Flash Malformed Header Overflow

Release Date: August 8, 2002

High (Remote Code Execution)

Systems Affected:
Macromedia Shockwave Flash - All Versions;
Unix and Windows; Netscape and Internet Explorer

While working on some pre-release eEye Retina CHAM tools, an exploitable
condition was discovered within the Shockwave Flash file format called SWF
(pronounced "SWIF").

Since this is a browser based bug, it makes it trivial to bypass firewalls
and attack the user at his desktop. Also, application browser bugs allow you
to target users based on the websites they visit, the newsgroups they read,
or the mailing lists they frequent. It is a "one button" push attack, and
using anonymous remailers or proxies for these attacks is possible.

This vulnerability has been proven to work with all versions of Macromedia
Flash on Windows and Unix, through IE and Netscape. It may be run wherever
Shockwave files may be displayed or attached, including: websites, email,
news postings, forums, Instant Messengers, and within applications utilizing
web-browsing functionality.

Technical Description:
The data header is roughly made out to:

[Flash signature][version (1)][File Length(A number of bytes too
short)][frame size (malformed)][Frame Rate (malformed)][Frame Count

By creating a malformed header we can supply more frame data than the
decoder is expecting. By supplying enough data we can overwrite a function
pointer address and redirect the flow of control to a specified location as
soon as this address is used. At the moment the overwritten address takes
control flow, an address pointing to a portion of our data is 8 bytes back
from the stack pointer. By using a relative jump we redirect flow into a
"call dword ptr [esp+N]", where N is the number of bytes from the stack
pointer. These "jump points" can be located in multiple loaded dll's. By
creating a simple tool using the debugging API and ReadMemory, you can
examine a process's virtual address space for useful data to help you with
your exploitation.

This is not to say other potentially vulnerable situations have not been
found in Macromedia's Flash. We discovered about seventeen others before we
ended our testing. We are working with Macromedia on these issues.

Retina(R) Network Security Scanner already scans for this latest version of
Flash on users' systems. Ensure all users within your control upgrade their

Vendor Status:
Macromedia has released a patch for this vulnerability, available at:

Discovery: Drew Copley
Exploitation: Riley Hassell

Greetings: Hacktivismo!, Centra Spike

Copyright (c) 1998-2002 eEye Digital Security
Permission is hereby granted for the redistribution of this alert
electronically. It is not to be edited in any way without express consent of
eEye. If you wish to reprint the whole or any part of this alert in any
other medium excluding electronic medium, please e-mail for

The information within this paper may change without notice. Use of this
information constitutes acceptance for use in an AS IS condition. There are
NO warranties with regard to this information. In no event shall the author
be liable for any damages whatsoever arising out of or in connection with
the use or spread of this information. Any use of this information is at the
user's own risk.

Please send suggestions, updates, and comments to:

eEye Digital Security