The bad news: The number of reported security vulnerabilities out in cyberspace is still growing. The good news: That growth has slowed significantly over last year.

Researchers say the number of bugs reported so far this year has increased by about 5 percent, versus the 40- to 60-percent spike seen in 2006.

Mitre, which officially tracks publicly reported bugs under the Common Vulnerability and Exposures (CVE) program, has seen only a 5 percent increase through April, with 2,245 vulnerabilities reported, versus the 60 percent jump last year at the same time, with 2,143. IBM-ISS's X-Force team, meanwhile, reported around 2,419 bugs last year through mid-May and 2,553 this year. It reported an overall 39.5 percent jump for all of 2006 over 2005.

So is the number of software bugs really shrinking, or are we merely waiting for the other shoe to drop?

The numbers will still break last year's record, predicts Gunter Ollmann, director of security strategy for IBM-ISS. "But [it] will still be [relatively] modest this year," he says. "I think we're looking at 8,500 publicly disclosed vulnerabilities" overall for 2007, up from 7,247 last year.

A combination of factors have contributed to the radical slowdown in bug reports, experts say. More researchers getting "real" jobs with vendors, some of which just patch and never actually disclose the offending bugs. There has been a slowdown in the reporting of simple bugs in less-popular software. And the black market is paying big bucks for zero-day exploits.

High-profile bugs represent about only 20 percent of Mitre's total vulnerabilities reported, says Steve Christey, principal information security engineer for Mitre, who also noted that the 40- to 60-percent increase last year might have been due in part to improvements in the CVE analysis process.

Other forces could also be at work. "In the past couple of years, it seems like there's been a huge increase of independent researchers who use basic techniques to find simple vulnerabilities in software that's not very popular," Christey says. "Maybe we've reached a critical mass in which there are finally enough independent researchers to provide basic evaluations of most software that's available on the Internet."

And there's typically a sharp increase in bug disclosures when researchers first start working on a new class of products, which typically are loaded with easy-to-find bugs, Christey says. "We haven't seen a new product class dominate the landscape since file format vulnerabilities in image or document processing products," he says. "There hasn't been a real 'fad' since file-format vulnerabilities, but ActiveX controls show some potential."

The numbers could jump again once researchers start hammering away at software that hasn't yet been widely deployed, Christey says.

Ollmann says Microsoft’s Windows Vista and Office 2007 may have slowed things a bit, too, with their new security features that prevent some typical bugs from actually becoming exploitable vulnerabilities. A newbie hacker can't just point a fuzzer at this new generation of software, he says. And Vista-compatible apps have not yet arrived in full force, either, which may also be contributing to the slowdown in bug finds. (See Bugs With No Bite.)

The research market is changing, too, Ollmann says. "Three to five years ago, a lot of upcoming new researchers' goals were to find and publicly disclose bugs and get credit for them. They found there was money in this by offering their services commercially." Some vendors are tapping these third-party researchers for bug finds, so disclosures aren't made until after the vendor has patched its product -- or are never disclosed at all, he adds.

Other vulnerabilities currently take special expertise to uncover. "Some relatively new vulnerability types remain the exclusive domain of the expert researcher, such as integer overflows and subtle buffer overflow variants," Christey says. "When knowledge and techniques for these new types becomes more accessible to the general researcher, we might see another increase."

And once the relatively slower summer months melt away into the fall, look out: That's the time of year when bug disclosures typically increase. "There's a lot of pickup following summer vacations, and holidays... especially the ones irresponsibly disclosed," Ollmann says. "The major vendors' [disclosures] are spread throughout the year."

Still, the early slowdown so far this year did catch researchers by surprise. "I'm a little surprised, but after the growth rates of the recent past, there's always hope that the bleeding will slow down," Christey says. "If there's one thing I've learned in this business, it's to expect the unexpected. Numbers ebb and flow all the time."

— Kelly Jackson Higgins, Senior Editor, Dark Reading