Yahoo Plugs Security Hole in Web Mail Service

Yahoo has fixed a security vulnerability in its Yahoo Mail service that could have allowed malicious hackers to hijack accounts and harm users in a variety of ways.

"We have developed a fix for this bug and have deployed it worldwide. Yahoo Mail users will not be required to take any action to be protected from this exploit," said Kelley Podboy, a Yahoo spokeswoman, via e-mail.

Nir Goldshlager and Roni Bachar from Avnet, a computer security company based in Israel, discovered the vulnerability in early August.

The problem was Yahoo Mail’s handling of attachments. By creating an HTML attachment with different encoding schemes, one could have bypassed Yahoo Mail’s security filter and executed malicious JavaScript code, Bachar said via e-mail.

The exploit allowed the JavaScript code to be executed as soon as a recipient opened the e-mail message, even if the recipient didn’t open the attachment.

It was also possible to steal the recipient’s Yahoo Mail cookie, hijack the session and gain access to the person’s inbox. "This attack vector could be used to launch a variety of other more sophisticated attacks," Bachar wrote. These could include unleashing worms, installing keylogger programs, phishing and scanning ports on the PC.

After identifying the vulnerability, Bachar and Goldshlager immediately alerted Yahoo, so that the vendor could patch its system. Bachar isn’t aware of any known exploits of the vulnerability.

-Juan Carlos Perez, IDG News Service (Miami Bureau)

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