This Joint Cybersecurity Advisory was coauthored by the U.S. Cybersecurity and Infrastructure Security Agency (CISA), the Australian Cyber Security Centre (ACSC), the United Kingdom’s National Cyber Security Centre (NCSC), and the U.S. Federal Bureau of Investigation (FBI).
This advisory provides details on the top 30 vulnerabilities—primarily Common Vulnerabilities and Exposures (CVEs)—routinely exploited by malicious cyber actors in 2020 and those being widely exploited thus far in 2021.
Cyber actors continue to exploit publicly known—and often dated—software vulnerabilities against broad target sets, including public and private sector organizations worldwide. However, entities worldwide can mitigate the vulnerabilities listed in this report by applying the available patches to their systems and implementing a centralized patch management system.
In 2020, cyber actors readily exploited recently disclosed vulnerabilities to compromise unpatched systems. Based on available data to the U.S. Government, a majority of the top vulnerabilities targeted in 2020 were disclosed during the past two years. Cyber actor exploitation of more recently disclosed software flaws in 2020 probably stems, in part, from the expansion of remote work options amid the COVID-19 pandemic. The rapid shift and increased use of remote work options, such as virtual private networks (VPNs) and cloud-based environments, likely placed additional burden on cyber defenders struggling to maintain and keep pace with routine software patching.
Four of the most targeted vulnerabilities in 2020 affected remote work, VPNs, or cloud-based technologies. Many VPN gateway devices remained unpatched during 2020, with the growth of remote work options challenging the ability of organization to conduct rigorous patch management.
CISA, ACSC, the NCSC, and FBI consider these vulnerabilities to be the topmost regularly exploited CVEs by cyber actors during 2020.
In 2021, malicious cyber actors continued to target vulnerabilities in perimeter-type devices. Among those highly exploited in 2021 are vulnerabilities in Microsoft, Pulse, Accellion, VMware, and Fortinet.
CISA, ACSC, the NCSC, and FBI assess that public and private organizations worldwide remain vulnerable to compromise from the exploitation of these CVEs. Malicious cyber actors will most likely continue to use older known vulnerabilities, such as CVE-2017-11882 affecting Microsoft Office, as long as they remain effective and systems remain unpatched. Adversaries’ use of known vulnerabilities complicates attribution, reduces costs, and minimizes risk because they are not investing in developing a zero-day exploit for their exclusive use, which they risk losing if it becomes known.
Organizations are encouraged to remediate or mitigate vulnerabilities as quickly as possible to reduce the risk of exploitation. Most can be remediated by patching and updating systems. Organizations that have not remediated these vulnerabilities should investigate for the presence of IOCs and, if compromised, initiate incident response and recovery plans. See the Contact Information section below for how to reach CISA to report an incident or request technical assistance.