A vulnerability in Microsoft's Internet Explorer browser could be a powerful new tool for spammers, allowing them to convincingly mask the real origin of web pages used to trick targets into revealing sensitive information.
The glitch allows attackers to use a specially crafted URL (uniform resource locator) to display in Internet Explorer's address field a domain name different from the web page's actual location, a practice known as "spoofing".
Spoofing is a favourite tactic of spammers hoping to con users out of passwords and other personal details with e-mails pretending to be from banks, e-commerce sites, software suppliers and other trusted institutions.
The security hole was first publicised in a posting to BugTraq, a mailing list for discussion of security vulnerabilities.
The post's author set up an illustration of the bug at www.zapthedingbat.com/security/ex01/vun1.htm. Security services firm Secunia issued its own advisory on the loophole, rating it a "moderately critical" threat.
The vulnerability afflicts several versions of Internet Explorer, including a fully patched edition of the software's latest release. Several other popular browsers, including Mozilla and Opera, are not affected and correctly display the actual location of sites taking advantage of the URL hack.
Microsoft said it is investigating reports of the vulnerability. When that inquiry is complete, the company will take whatever steps it deems necessary, such as issuing a patch.
Standard PC-protection practices such as anti-virus software and firewalls may not help in thwarting exploitation of the Internet Explorer bug, since it relies on social engineering rather than a technical attack.
Secunia recommended in its advisory that users avoid following links from untrusted sources. Firewalls with URL-filtering capabilities may also defeat the vulnerability.
Microsoft said it has not received any reports of the glitch being exploited, and objected to the bug's disclosure on the BugTraq mailing list before it had been notified.
"We continue to encourage the responsible disclosure of vulnerabilities. We believe the commonly accepted practice of reporting vulnerabilities directly to a supplier serves everyone's best interests," a spokeswoman said.
Stacey Cowley writes for IDG News Service