Research Archives > Security Advisories > AD20020808b

Macromedia Shockwave Flash Malformed Header Overflow

Release Date:
8/8/2002 12:00:00 AM

Date Reported:
8/8/2002 12:00:00 AM

Severity:
High

Vendor:
Macromedia

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

Overview:
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 Details:
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 (malformed)][Data]

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.

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

Vendor Status:
Macromedia has released a patch for this vulnerability, available at:
http://www.macromedia.com/v1/handlers/index.cfm?ID=23293&Method=Full&Title=MPSB02%2D09%20%2D%20Macromedia%20Flash%20Malformed%20Header%20Vulnerability%20Issue&Cache=False

Credit:
Discovery: Drew Copley Exploitation: Riley Hassell

Greetings:
Hacktivismo!, Centra Spike

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