Beware of the Quiet Ones

Cross-site scripting (XSS) may be the poster child for what's wrong with Web security, but an updated vulnerability report from Mitre suggests that two lesser-known attack vectors are quietly growing as well.

Mitre has quietly released the final version of its 2006 Common Vulnerabilities and Exposures (CVE) report, which it previewed last fall. As the company reported previously, XSS was the number one vulnerability for 2006, usurping SQL injection for the first time.

But there are also a couple of surprises in the updated report. For example, PHP Remote File Inclusion (a.k.a. PHP RFI, or php-include) jumped from a number four ranking to number three for the year. PHP RFI vulnerabilities in 2006 increased 1,000 percent from the previous year, and they now account for 13.1 percent of all reported flaws. This puts PHP RFI just behind the better-known SQL injection (13.6 percent). (See Cross-Site Scripting: Attackers' New Favorite Flaw.)

The updated report also flags cross-site request forgery (CSRF) as a vulnerability to watch, even though it accounts for less than .1 percent of bugs reported. "There is a real disconnect here between what Web app security researchers are finding on the professional auditing side versus what's being publicly recorded in the CVE," says Steven Christey, principal information security engineer for Mitre. "Researchers who publicly disclose [vulnerabilities] just aren't looking for [CSRF bugs]."

But Christey says that doesn't mean Web developers and operators should ignore CSRF. Like other researchers, he calls CSRF a "sleeping giant" that may be more prevalent than reported. "It's a little more complex than most kinds of vulnerabilities," he says. "And its implications might not immediately be as obvious to someone who discovers it." (See Killer Combo: XSS + CSRF and CSRF Vulnerability: A 'Sleeping Giant'.)

Kris Kendall, principal consultant for Mandiant, says although his company regularly finds CSRF bugs in penetration tests, he rarely sees actual attacks. Still, it's a potentially dangerous attack vector for stealthy, targeted attacks. "CSRF has a larger impact for the victim than a typical XSS attack," he says. "And mitigation is tricky -- it's hard to fix."

PHP, on the other hand, is low-hanging fruit for attackers. Kendall says an attacker can basically Google to find Websites vulnerable to the PHP RFC bug. PHP lets an attacker take over a machine, and some researchers say it's becoming popular among botnet herders who use it for command and control functions.

"I would think these vulnerabilities would not so much be used to add new bots, but to help Botherders manage their existing bots... adding new command and control nodes," Kendall says.

The best way to protect against an attack is to disable the "registered globals" feature in PHP, Kendall says. But not all organizations do this, he notes.

"RFI is extremely powerful and easy to use, so it's no surprise it's attractive to attackers," says Mitre's Christey. And many Web hosting firms leave the registered globals feature enabled, he notes, which leaves their customers at risk.

Web application security vulnerabilities are the hot ticket now, and the CVE, which is sponsored by the Department of Homeland Security, reflects that. Mitre's report also demonstrates that it's not just the popular bugs that must be addressed, says Robert Martin, lead for compatibility and outreach at Mitre. "There are other more complex and dangerous types of errors you need to be aware of to prevent and remove."

Christey and Martin say they haven't analyzed the 2007 CVE numbers by bug as yet. But Mitre says so far there have been 2,245 vulnerabilities reported the first half of this year, just slightly ahead of last year this time, which was 2,143. That represents a drastic drop in the rate of growth of bug disclosures, but researchers still expect this year to break last year's record. (See Bug Disclosures Decline.)

— Kelly Jackson Higgins, Senior Editor, Dark Reading