The number of vulnerabilities disclosed to the public initially declined in 2020 but, by the end of the year, caught up to within 1% of the total number of flaws reported in 2019, according to data published on Thursday by Risk Based Security, a vulnerability intelligence firm.

Overall, companies and researchers published information on at least 23,269 software flaws in 2020, but the number of reported vulnerabilities initially lagged behind the previous year's numbers by more than 10% in the first quarter. While the reason for the initial disruption in the number of reported issues remains unclear, a variety of factors could have come into play — from layoffs of security researchers, to additional security work, to disruptions in the reporting process, says Brian Martin, vice president of vulnerability intelligence at Risk Based Security.

"The statistics support that COVID did influence disclosure to some degree," Martin says. "We still do not know how, or in what ways — whether due to work from home or layoffs. There are a lot of things that could have affected vulnerability disclosures."

In addition to documenting the effects of the pandemic on vulnerability disclosure, the annual report also found that researchers had increasingly focused on finding security issues in Microsoft's core operating systems. In 2020, four versions of the Windows operating system made the top 10 list for reported vulnerabilities, a reversal from 2019, when no Windows products made the list.

"Windows was the real standout," Martin says. "The increases are definitely in line with what we saw in terms of Patch Tuesdays getting bigger."

Patch Tuesdays are the second Tuesday of the month, on which Microsoft has traditionally — since 2003 — regularly released patches. Other software vendors, such as Adobe and Oracle, often release on the same day. When a handful of vendors all release patches, security administrators may have to deal with applying updates to close hundreds of vulnerabilities. On April 14, 2020, for example, vendors released patches for 522 issues, according to Risk Based Security.

The increasing number of vulnerabilities raises concerns about how much security efforts have paid off, says Martin. Microsoft has implemented its Secure Development Lifecycle (SDLC), instituted bug bounties, and conducted more automated testing, but the consistently high number of vulnerabilities suggests that such processes aren’t having as much impact. An alternative explanation is that the codebase has expanded, so that even cleaner code results in an overall plateau in the number of issues.

"The question that many people are asking is: Where is this greener pasture, when all of our work pays off and we get fewer vulnerabilities?" he says. 

The news is not all bad. Reported vulnerabilities are generally fixed more quickly and exploiting the issues has become more difficult, Martin says. "To some degree, it is working — usually, exploiting a single vulnerability is not enough. Instead, it takes chaining exploits for three vulnerabilities together, but the number of vulnerabilities has not declined," he says.

Risk Based Security typically uncovers more issues than tracked in the National Vulnerability Database (NVD), an online collection — maintained by the US National Institute of Standards and Technology (NIST) — of information of software flaws that have been assigned a Common Vulnerability and Exposures (CVE) identifier. 

In the past four years, driven by changes in the CVE process, the number of vulnerabilities added to the NVD shot up each year, more than doubling in 2017 to top 14,600 reported issues, up from nearly 6,500 issues the previous year. Since then, the volume of vulnerabilities has slowly climbed, reaching 18,353 published flaws in 2020. 

Risk Based Security has published a roughly similar volume of vulnerabilities for the past four years, ranging from 22,665 in 2017 to a high of 23,508 in 2018. 

The company notes that more vulnerabilities are being reported in mobile operating systems and applications. Android and Google mobile software have landed on the top 10 list of vulnerable operating systems.

"That little phone you are carrying in your pocket is now seeing as many vulnerabilities as the large software systems are," Martin says. "It is becoming increasingly important that you patch your devices as soon as possible."

For companies, the expanding vulnerability surface area means that, without prioritization, companies are now having a hard time focusing on the vulnerabilities that pose the most risk, he says.

"So, we are still left with a whack-a-mole game," Martin says, "where you have to prioritize vulnerabilities and rely on defense in depth to make sure that any compromise is quickly stopped."