Top 10 Routinely Exploited Vulnerabilities

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Summary

The Cybersecurity and Infrastructure Security Agency (CISA), the Federal Bureau of Investigation (FBI), and the broader U.S. Government are providing this technical guidance to advise IT security professionals at public and private sector organizations to place an increased priority on patching the most commonly known vulnerabilities exploited by sophisticated foreign cyber actors.

This alert provides details on vulnerabilities routinely exploited by foreign cyber actors—primarily Common Vulnerabilities and Exposures (CVEs)[1]—to help organizations reduce the risk of these foreign threats.

Foreign cyber actors continue to exploit publicly known—and often dated—software vulnerabilities against broad target sets, including public and private sector organizations. The exploitation of these vulnerabilities often requires fewer resources as compared with zero-day exploits for which no patches are available.

The public and private sectors could degrade some foreign cyber threats to U.S. interests through an increased effort to patch their systems and implement programs to keep system patching up to date. A concerted campaign to patch these vulnerabilities would introduce friction into foreign adversaries’ operational tradecraft and force them to develop or acquire exploits that are more costly and less widely effective. A concerted patching campaign would also bolster network security by focusing scarce defensive resources on the observed activities of foreign adversaries.

For indicators of compromise (IOCs) and additional guidance associated with the CVEs in this Alert, see each entry within the Mitigations section below. Click here for a PDF version of this report.

Technical Details

Top 10 Most Exploited Vulnerabilities 2016–2019

U.S. Government reporting has identified the top 10 most exploited vulnerabilities by state, nonstate, and unattributed cyber actors from 2016 to 2019 as follows: CVE-2017-11882, CVE-2017-0199, CVE-2017-5638, CVE-2012-0158, CVE-2019-0604, CVE-2017-0143, CVE-2018-4878, CVE-2017-8759, CVE-2015-1641, and CVE-2018-7600.

  • According to U.S. Government technical analysis, malicious cyber actors most often exploited vulnerabilities in Microsoft’s Object Linking and Embedding (OLE) technology. OLE allows documents to contain embedded content from other applications such as spreadsheets. After OLE the second-most-reported vulnerable technology was a widespread Web framework known as Apache Struts.
  • Of the top 10, the three vulnerabilities used most frequently across state-sponsored cyber actors from China, Iran, North Korea, and Russia are CVE-2017-11882, CVE-2017-0199, and CVE-2012-0158. All three of these vulnerabilities are related to Microsoft’s OLE technology.
  • As of December 2019, Chinese state cyber actors were frequently exploiting the same vulnerability—CVE-2012-0158—that the U.S. Government publicly assessed in 2015 was the most used in their cyber operations.[2] This trend suggests that organizations have not yet widely implemented patches for this vulnerability and that Chinese state cyber actors may continue to incorporate dated flaws into their operational tradecraft as long as they remain effective.
  • Deploying patches often requires IT, security professionals, to balance the need to mitigate vulnerabilities with the need for keeping systems running and ensuring installed patches are compatible with other software. This can require a significant investment of effort, particularly when mitigating multiple flaws at the same time.
  • A U.S. industry study released in early 2019 similarly discovered that the flaws malicious cyber actors exploited the most consistently were in Microsoft and Adobe Flash products, probably because of the widespread use of these technologies.[3]  Four of the industry study’s top 10 most exploited flaws also appear on this Alert’s list, highlighting how U.S. Government and private-sector data sources may complement each other to enhance security.

Vulnerabilities Exploited in 2020

In addition to the top 10 vulnerabilities from 2016 to 2019 listed above, the U.S. Government has reported that the following vulnerabilities are being routinely exploited by sophisticated foreign cyber actors in 2020:

  • Malicious cyber actors are increasingly targeting unpatched Virtual Private Network vulnerabilities.
    • An arbitrary code execution vulnerability in Citrix VPN appliances, known as CVE-2019-19781, has been detected in exploits in the wild.
    • An arbitrary file reading vulnerability in Pulse Secure VPN servers, known as CVE-2019-11510, continues to be an attractive target for malicious actors.
  • March 2020 brought an abrupt shift to work-from-home that necessitated, for many organizations, rapid deployment of cloud collaboration services, such as Microsoft Office 365 (O365). Malicious cyber actors are targeting organizations whose hasty deployment of Microsoft O365 may have led to oversights in security configurations and vulnerable to attack.
  • Cybersecurity weaknesses—such as poor employee education on social engineering attacks and a lack of system recovery and contingency plans—have continued to make organizations susceptible to ransomware attacks in 2020.

Mitigations

This Alert provides mitigations for each of the top vulnerabilities identified above. In addition to the mitigations listed below, CISA, FBI, and the broader U.S. Government recommend that organizations transition away from any end-of-life software.