The U.S. government site that tracks cyber security risks was recently found vulnerable to cross-site scripting, a technique commonly used in hacker attacks and web site spoofing. Several security sites have published a demonstration of the security hole in the web site for the National Institute of Standards and Technology (NIST), which hosts the U.S. National Vulnerability Database, which ironically includes numerous examples of cross-site scripting.
Cross-site scripting (XSS) is a well known technique which involves injecting the text of code to be executed by the browser into urls that generate dynamic pages. Attacks using XSS have been found by security researchers in a wide variety of products and specific sites in recent years. The cross-site scripting vulnerability in the NIST site was found in a script that warns visitors that they are about to leave the NIST site, a common practice on U.S. government sites. The NIST script allows potentially malicious Javascript to be appended to the URL and executed by the browser, a technique which works in Firefox and Internet Explorer. The flaw was originally reported by the RootShell Security Group. Staff at the NIST web site closed the security hole after being contacted by people who saw the RootShell posting.
The Netcraft Toolbar blocks common cross-site scripting attacks, protecting users from coding weaknesses in trusted sites, including the NIST flaw. "That was the first time when a trusted, security-related site generated a Block XSS? message to me," noted security researcher Juha-Matti Laurio, a frequent contributor to security community resources on the web.
Web programmers can prevent most cross-site scripting attacks by validating form input and potential modifications to URLs, and ensuring that all user data is correctly encoded before it is displayed or stored.