Advisory: Malformed GIF images could allow execution of arbitrary code
When loading GIF images into memory, Opera should allocate the correct amount of memory to store that image. Specially crafted image files can cause Opera to allocate the wrong amount of memory. Subsequent data may then overwrite unrelated memory with attacker-controlled data. This can lead to a crash, which may also execute that data as code.
Opera Software has released Opera 12.12, where this issue has been fixed.