.ANI files are commonly used by web developers to display custom cursor animations to enhance web-site experiences.
An unspecified vulnerability exists within Microsoft Windows which may possibly allow for a remote attacker to execute arbitrary code under the context of the logged in user. This vulnerability requires user interaction by viewing a malicious Windows animated cursor (.ANI) file.
The most potent attack method is by embedding a malicious .ANI file within an HTML web page. Doing so allows the vulnerability to be exploited with minimal user interaction by simply coaxing a user to follow a hyperlink and visit a malicious web site. Other exploit vectors exist including Microsoft Office applications since they also rely on the same .ANI processing code, making e-mail delivery also a potent threat by using Microsoft Office attachments.
Since .ANI processing is performed by USER32.dll and not the attack vector application itself, all attack vectors have the potential to use a similar exploit with similar address offsets targeted at Windows directly, allowing for a very reliable exploit.
NOTE: This advisory information is gathered from the references below.
Arbitrary code execution under the context of the logged in user.
A web browser remote code execution vulnerability has a very high impact since the source of the malicious payload can be any site on the Internet. An even more critical problem is generated when clients are administrators on their local hosts, which would run the malicious payload with Administrator credentials. Exploitation impact can vary from the reported trojan installation to full system compromise by coupling this attack with a privilege escalation vulnerability to acquire SYSTEM access.
eEye Digital Security's Research Team has released a workaround for the zero-day vulnerability as a temporary measure for customers who have not yet installed Blink. Blink generically protects from this and other vulnerabilities without the need for updating and is available for free for personal use on all affected platforms except for Vista. This workaround is not meant to replace the forthcoming Microsoft patch, but rather as a temporary mitigation against this flaw.
The temporary patch mitigates this vulnerability by preventing cursors from being loaded outside of %SystemRoot%. This disallows websites from loading their own, potentially malicious animated icons, while causing little to no business disruption on hosts with the patch installed.
Organizations that choose to employ this workaround should take the steps required to uninstall it once the official Microsoft patch is released. More information regarding installation and uninstallation is available in the patch installer. Please note that at this time this workaround supports all affected platforms except for x64 and Itanium architectures.