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Google has patched a hole in its search engine that could have allowed malicious hackers to modify the content of the Google search results page or silently modify search results. And the company says it is dealing now with a second, similar flaw.

This development comes in a week when Google's new desktop search program took some heat from privacy and security experts, who say it poses risks for users who don't understand its power.

The first vulnerability concerns the Google Custom WebSearch service, which allows third-party Web portals and other Web sites to use Google's servers to search content on their Web site. A flaw in Google's Web servers allowed malicious hackers to insert JavaScript instead of links to image files, permitting them to alter the appearance of the Google search results page or to steal search data. After being alerted to the hole, Google fixed the vulnerability, says Nathan Tyler, a Google spokesperson.

"Google was recently alerted to a potential security vulnerability affecting users of our Web site. We have since fixed this vulnerability, and all current and future Google.com users are protected," Tyler says.

The company is also aware of a second vulnerability, discovered by UK security firm Netcraft Ltd., and will be fixing its systems shortly to remove the vulnerability, he says.

The Custom WebSearch vulnerability was first reported in the online security newsgroup Bugtraq. Google's servers fail to validate URLs for image files to make sure they actually point to images. Malicious hackers could trigger the vulnerability using a Google custom search form, or even through a customized HTML link, by feeding Google's servers computer script instead of an image URL, according to the notice's author, who used the name "Jim Ley."

When Did Google Know?

According to the notice's author, the Custom WebSearch vulnerability has existed for around two years without being fixed by Google, which was notified twice of the hole. The recent release of the Desktop Search tool from Google worsened the impact of the flaw, allowing hackers to leverage the feature to search for and steal content, such as passwords or personal financial information, from files on a local hard drive. A number of major Web sites use the Google Custom WebSearch service, including those of Netscape Communications, the Washington Post, and Virgin.net, according to Google's Web page.

In another example of how the flaw could be used, Ley posted a link on his Web site that replaced Google's main page with a page announcing that Google was becoming a for-fee search service and asking visitors to provide credit card information to sign up for the service.

The Google hole is an example of a common security problem affecting Web sites that dynamically generate Web pages based on input from unknown sources, such as Web surfers, according to a vulnerability note written in 2000 by the Computer Emergency Readiness Team at Carnegie Mellon University in Pittsburgh.

Google developers appear to have missed that four-year-old warning, and the company did not respond to repeated e-mail messages sent to an address for reporting security holes, Ley said.

In patching it, Google developers changed their code to prevent JavaScript and VBScript, but may have left open other avenues of attack, Ley wrote in an e-mail.

"The problem with this approach is that it relies on them thinking of every possible thing they could exclude.... There's so many ways to execute script, attempting to cover all the bases with this approach is risky," he wrote.

Malicious Content Entry

However, even as the company patched one hole, security firm Netcraft said it discovered a different vulnerability that could allow attackers to inject malicious content in the Google Web site for online identity-theft scams or other purposes.

The new hole is a script injection hole similar to the one reported by Ley, and was found in a Google search feature that is accessible by anybody, says Paul Mutton, an Internet services developer at Netcraft.

Like the vulnerability reported in Bugtraq, the new hole allows malicious hackers to use script to replace the content of the Google search results page, and could be used to trick users into trusting the content displayed, Mutton says.

The Bath, UK, company does not want to discuss specific details about the vulnerability. Mutton notified Google and was informed that the hole will be patched this week, he says.