Re: EEYE: Macromedia Shockwave Flash Malformed Header Overflow

[Will Bryant <will () core-dev co nz>]

> I've downloaded this fixed version, but it seems to be vulnerable to
> something I've discovered last week: if you take a .swf and rot13 encode
> it (not all of it, so the headers are not messed up), you can crash the
> user's browser.

There are quite literally a thousand ways to crash the Macromedia Flash 
player (at least the version in use a year ago, when I was dealing with 
it).  The majority of mistakes one makes, and bugs one finds, when 
attempting to create an SWF-writing application will kill the player: about 
a quarter of them will crash the player (and browser), the remainder mostly 
cause the player's memory usage to shoot up to about 40-70mb and then hang.

A surprisingly large number of these faults can be triggered just using the 
Macromedia SWF SDK, without any mucking around with the binary SWF files, 
although you do have to fix a number of bugs in the SDK before you can get 
to that stage (which I won't go into here - Macromedia seem to have made a 
habit of suing anyone who tries to distribute bugfixes for their SDK).

Anyway, getting back to the security issues, while crashing the browser is 
definitely unacceptable I'm not yet sure if any of those crashes would be 
exploitable, as most of them seem to be due to problems with their 
algorithms (as opposed to say simple string buffer overflows) - stack 
overflows due to recursion, null pointer violations, that kind of thing.

Further experimentation would be warranted.  I'd recommend starting with 
the audio compression, image compression, and font handling, as since they 
involve buffer decompression etc. there's a better chance they're 
susceptible to buffer overflows.

Cheers,
Will

_______________________________________________________________________
Will Bryant, will () core-dev co nz                    cell +64 21 655 443
http://www.core-dev.co.nz/             Personal: http://carcino.gen.nz/
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