What is it?
A 0-day vulnerability that affects all supported versions of Internet Explorer and can be exploited to compromise a user's system.
How does it work?
The vulnerability is caused by a use-after-free error when handling the “execCommand” method and can be exploited to dereference an already freed CMshtmlEd object in memory to gain control of the program flow. This allows executing arbitrary code on a user's system with the user's privileges.
Should I be worried?
Users should show extreme caution when visiting untrusted web sites if their systems are not fully patched.
How can I prevent it?
Shortly after information on the 0-day was released, Microsoft confirmed the vulnerability via a security advisory and provided a temporary Fix-it solution. On Sept. 21, Microsoft released an out-of-band security bulletin, MS12-063, which addressed the 0-day vulnerability along with four other potential remote code execution bugs.