Sophisticated advanced persistent threat groups are no longer the only ones leveraging zero-day exploits.
An analysis by FireEye of exploit activity last year showed that more cyberattackers exploited more zero-day vulnerabilities in 2019 than in any of the previous three years.
While known threat groups accounted for a substantial portion of the activity, FireEye found that a wide range of other groups leveraged zero-day exploits as well. In particular, researchers from FireEye observed a significant increase over time in zero-day exploit activity by international governments, US and other law enforcement agencies, and other customers of companies selling offensive cyber weapons.
"From 2012 to 2016, the actors most frequently using zero-days tended to be among the most sophisticated," says Kelli Vanderlee, manager of intelligence analysis at FireEye Mandiant.
But since about 2017, the field has substantially diversified, at least partially due to the role of vendors offering offensive cyber threat capabilities.
Examples of such vendors include the Hacking Team of Italy, NSO Group based in Israel, and Gamma International in the UK. Such firms have been observed selling cyber espionage and intrusion software and services — including zero-day exploits to governments and other entities for several years. Those that are said to have benefited from these tools include governments with dubious human rights records such as Sudan, Ethiopia, and Uzbekistan, Vanderlee says.
In 2019, tools provided by such private cyber offensive security firms were used in multiple attacks, according to FireEye.
Examples include a zero-day exploit in WhatsApp (CVE-2019-3568) that was used to distribute spyware developed by the NSO Group and an attack on a Russian healthcare organization that involved the use of a 2018 Adobe Flash zero-day (CVE-2018-15982). Another example was an Android zero-day bug (CVE-2019-2215) that attackers exploited using NSO group tools, FireEye said in a report summarizing its analysis this week.
The trend "suggests that zero-day use may no longer be an important indicator of sophistication," Vanderlee says. "Rather, it seems to be a more reliable indicator of access to resources."
Financially motivated groups too have been steadily ramping up their use of zero-day exploits though not quite to the level as espionage groups, FireEye said. As one example, the security vendor pointed to a targeted intrusion in February 2019, where attack group FIN6 exploited a zero-day vulnerability in Windows server software.
The increased use of zero-day exploits — and the wider range of threat actors that are using these tools could prove troublesome for enterprise organizations. According to FireEye, the number of adversaries that leverage zero-day exploits will almost certainly increase over the next few years and at a faster rate than their overall cyber offensive skills. The only thing that is going to limit their access to these tools will be the necessary funds.
"As access to zero-days becomes more widespread, enterprises must compare the full range of techniques used by attackers known to target them against existing controls and strategies," Vanderlee says. "While exploitation of a zero-day vulnerability gives attackers a significant advantage, a defense-in-depth approach may allow defenders to disrupt and defeat malicious operations at other stages of the attack life cycle," she notes.
One silver lining for defenders is that private companies are increasingly providing sophisticated tools to groups with limited overall capabilities and to groups with little regard for operational security. As a result, there is a higher chance that activity involving the use of zero-day bugs will be more easily observed, FireEye said in its report.