One day after Symantec researchers discovered software that attacked a critical unpatched vulnerability in RealNetworks' media player, Real says that a fix for the issue is imminent.

"Real has created a patch for RealPlayer 10.5 and RealPlayer 11 that addresses the vulnerability identified by Symantec," wrote RealNetworks general manager of product development Russ Ryan, in a Friday blog posting. "Real will make this patch available to users via this blog and our security update page later today."

Users of RealOne Player, RealOne Player v2, and RealPlayer 10 should upgrade to the 10.5 version of the product or the RealPlayer 11 beta code and should install the patch, Ryan said.

The attack exploits a flaw in an ActiveX browser helper object, software that RealPlayer employs to help users who are experiencing technical difficulties, so the PC must be using the Internet Explorer browser to be affected by this particular attack, Symantec said.

The attack only works on Windows systems, RealNetworks said. Linux, Mac, and RealPlayer 8 users are not affected.

Attackers were using a complicated network of advertising Web sites to launch the attack from a Web site that has been spotted hosting malicious code several times over the past two years, Symantec said.

"The exploit itself is embedded in advertisements that were being served by 247realmedia.com," Symantec said in a note on its DeepSight threat management system. "The redirection to the exploit page... was accomplished through an iFrame embedded in each advertisement."

iFrame is an HTML command that allows developers to insert a second Web page into the page being viewed. It is often used by malware creators because these iFrame pages can be as small as 1 pixel, making them invisible to the naked eye.

Users who do not have the patch can turn off ActiveScripting within IE as a workaround to the problem. Very technical users can also set kill bit on the Class identifier (CLSID) FDC7A535-4070-4B92-A0EA-D9994BCC0DC5 to disable the ActiveX control, Symantec said.