A public exploit code for a severe vulnerability affecting the Internet Explorer toolbar for business networking site LinkedIn, has been posted by a pair of security researchers.

The client-side ActiveX flaw, which garnered Secunia’s highest severity rating of "extremely critical," can permit an attacker to remotely execute arbitrary code, Jared DeMott, one of the vulnerability’s discoverers, told SCMagazine.com today.

Users are exploited when they visit a malicious website, according to a Secunia advisory. The bug is caused by an error in the toolbar when handling the "Search()" method.

DeMott said he decided to go public with the exploit after an official with LinkedIn, which has more than 12 million members, hung up on him. That is when he knew the vulnerability would end "0-day style," he said.

DeMott, who runs VDA Labs, said he called LinkedIn to either sell the bug or offer his company’s consulting services, like he does for any vendor impacted by a vulnerability discovered by DeMott or Seitz.

Kay Luo, spokeswoman for LinkedIn, told SCMagazine.com today that the company does not respond to researchers looking to profit off vulnerabilities.

She added that the only users affected are those who have downloaded the toolbar. The company does not disclose how many people use that feature.

"For it (the vulnerability) to be a risk, the user would have to be lured into navigating to a malicious website," Luo said. "Right now, we don’t have any reports of malicious exploits. We’re looking at it and taking it very seriously, but I think we’ll have it fixed shortly."

When LinkedIn did not respond to DeMott’s call, he said he had no choice but to publicly release the exploit.