Opera and FireFox contains vulnerable code for handling BMP files with partial palette. The code allows to craft a BMP file that leaks information from the heap. This information can be sent to remote server using <canvas> tag (HTML 5) and javascript. Also other browser (for example Apple Safari) contain vulnerable BMP handling code, but since there is no way of acquiring the image data (due to not all canvas method being implemented), it doesn’t pose a serious threat (hmm… then again, maybe the attacker could convince the user to do a screenshot and send it to the attacker 
As a matter of fact Apple Safari has a simillar problem with certain GIF files.
The BMP format has a field in the BITMAPINFOHEADER named biClrUsed,
The field says how many colors does the palette contain. If this field
is 0, then 256 color palette is used. When this field is not 0, the
palette has the given number of colors.
Both browsers either allocate to just the “right” amount of memory
(using the equation biClrUsed * sizeof(RGB)), or forget to zero the
allocated palette.
In this case, if a color from the upper (non existing or not zeroed)
part of the palette is used, soem information is copied to the screen
as a colorful pixel.
If the attacker creates a BMP file with biClrUser = 0, and fills it
with gradient, from 0 to 255: 00 01 02 03 04 05 … and so on, the
displayed BMP will in fact copy the palette to the screen, which of
course means that it copies the data lying on the heap to the screen.
The attacker could also use HTML 5 tag <canvas> to aquire pixel
color information from the bitmap, and then use javascript to post it
to a remote server.
The harvested data contains various information including parts of
other websites, users “favorites” and history, and other information.
This has been tested, a proof of concept exploit has been created, but
will not yet be released.
Versions affected and vendor status
FireFox 2.0.0.11 and prior that support canvas.getImageData or any
other method to aquire image data are affected.
The vendor was informed and has released a non vulnerable version
of the application - 2.0.0.12.
Opera 9.24 is not affected due to not supporting canvas.getImageData.
The newer beta versions are affected (9.50 beta).
The vendor was informed and has released a non vulnerable version
of the application - 9.25.Other vendors were also informed.
* Additional info
FireFox 2.0.0.11 may crash when using this vulnerability due to
heap boundary error (read access violation). So it is possible to
remotly crash the browser.* Video demonstration
Video demonstration of the vulnerability can be found on the following sites: http://blog.hispasec.com/lab/ http://vexillium.org/?sec-ff
