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What is a clipboard hijack attack?

A clipboard hijacking is an exploit in which the attacker gains control of the victim’s clipboard and replaces its contents with their own data, such as a link to a malicious Web site.

The attack makes it impossible for users to copy anything else to the clipboard until they either close the browser or reboot the machine. Aside from the nuisance factor, the danger is that a user might inadvertently paste the inserted content into their browser or into online content, exposing themselves or others to malicious code.

In August 2008, there were reports of clipboard hijack attacks conducted through Adobe Flash-based ads on many legitimate Web sites, including Digg, Newsweek and MSNBC.com. The coding is in Shockwave files and uses a method called System.setClipboard() that repeatedly flushes and replaces clipboard contents. If users follow the inserted link, they are taken to a fake security software site warning them that their systems are infested with malware. The purpose of the attack is to get users to download fraudulent software, putting personal information at risk in the process. All major operating systems and browsers are vulnerable to the attacks, as long as Flash is installed.

Adobe has since announced it will add a mechanism to the next version of Flash that allows users to grant or deny access when a Shockwave file tries to load data to the clipboard.