"A remote vulnerability exists in the QuickTime player for Windows XP and Vista (latest service packs)," said company founder Petko D. Petkov in a blog post. "An attacker could exploit the vulnerability by constructing a specially crafted QuickTime supported media file that allows remote code execution if a user visited a malicious Web site, opened a specially crafted attachment in e-mail, or opened a maliciously crafted media file from the desktop."
Petkov said that if the malicious file was opened by logged-in user with administrative privileges, the attacker could take control of the affected system.
"The vulnerability was successfully tested in Windows XP SP2 and Windows Vista SP1 environments," Petkov said, adding that other versions of QuickTime are believed to be exploitable too.
Petkov said that in keeping with responsible disclosure practices, his group will make the privately held vulnerability known to Apple. He did not say whether details of the attack would be made public after Apple has had a chance to patch the vulnerability.
GNU Citizen has posted a video demonstrating that attack on its Web site.
Earlier this month, Apple released QuickTime 7.4.5, which contained a dozen security fixes.
In January, Italian security researcher Luigi Auriemma posted a proof-of-concept exploit for a zero-day vulnerability in what was then the most current version of Apple's QuickTime media software (7.3.1).