SUMMARY

The following cybersecurity agencies coauthored this joint Cybersecurity Advisory (CSA):

• United States: The Cybersecurity and Infrastructure Security Agency (CISA), National Security Agency (NSA), and Federal Bureau of Investigation (FBI)
• Australia: Australian Signals Directorate’s Australian Cyber Security Centre (ACSC)
• Canada: Canadian Centre for Cyber Security (CCCS)
• New Zealand: New Zealand National Cyber Security Centre (NCSC-NZ) and Computer Emergency Response Team New Zealand (CERT NZ)
• United Kingdom: National Cyber Security Centre (NCSC-UK)

This advisory provides details on the Common Vulnerabilities and Exposures (CVEs) routinely and frequently exploited by malicious cyber actors in 2022 and the associated Common Weakness Enumeration(s) (CWE). In 2022, malicious cyber actors exploited older software vulnerabilities more frequently than recently disclosed vulnerabilities and targeted unpatched, internet-facing systems.

The authoring agencies strongly encourage vendors, designers, developers, and end-user organizations to implement the recommendations found within the Mitigations section of this advisory—including the following—to reduce the risk of compromise by malicious cyber actors.

• Vendors, designers, and developers: Implement secure-by-design and -default principles and tactics to reduce the prevalence of vulnerabilities in your software.
  • Follow the Secure Software Development Framework (SSDF), also known as SP 800-218, and implement secure design practices into each stage of the software development life cycle (SDLC). As part of this, establish a coordinated vulnerability disclosure program that includes processes to determine root causes of discovered vulnerabilities.
  • Prioritize secure-by-default configurations, such as eliminating default passwords, or requiring addition configuration changes to enhance product security.
  • Ensure that published CVEs include the proper CWE field identifying the root cause of the vulnerability.
• End-user organizations:
  • Apply timely patches to systems. Note: First check for signs of compromise if CVEs identified in this CSA have not been patched.
  • Implement a centralized patch management system.
  • Use security tools, such as endpoint detection and response (EDR), web application firewalls, and network protocol analyzers.
  • Ask your software providers to discuss their secure by design program and to provide links to information about how they are working to remove classes of vulnerabilities and to set secure default settings.

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TECHNICAL DETAILS

Key Findings

In 2022, malicious cyber actors exploited older software vulnerabilities more frequently than recently disclosed vulnerabilities and targeted unpatched, internet-facing systems. Proof of concept (PoC) code was publicly available for many of the software vulnerabilities or vulnerability chains, likely facilitating exploitation by a broader range of malicious cyber actors.

Malicious cyber actors generally have the most success exploiting known vulnerabilities within the first two years of public disclosure—the value of such vulnerabilities gradually decreases as software is patched or upgraded. Timely patching reduces the effectiveness of known, exploitable vulnerabilities, possibly decreasing the pace of malicious cyber actor operations and forcing pursuit of more costly and time-consuming methods (such as developing zero-day exploits or conducting software supply chain operations).

Malicious cyber actors likely prioritize developing exploits for severe and globally prevalent CVEs. While sophisticated actors also develop tools to exploit other vulnerabilities, developing exploits for critical, wide-spread, and publicly known vulnerabilities gives actors low-cost, high-impact tools they can use for several years. Additionally, cyber actors likely give higher priority to vulnerabilities that are more prevalent in their specific targets’ networks. Multiple CVE or CVE chains require the actor to send a malicious web request to the vulnerable device, which often includes unique signatures that can be detected through deep packet inspection.

Top Routinely Exploited Vulnerabilities

Table 1 shows the top 12 vulnerabilities the co-authors observed malicious cyber actors routinely exploiting in 2022:

• CVE-2018-13379. This vulnerability, affecting Fortinet SSL VPNs, was also routinely exploited in 2020 and 2021. The continued exploitation indicates that many organizations failed to patch software in a timely manner and remain vulnerable to malicious cyber actors.
• CVE-2021-34473, CVE-2021-31207, CVE-2021-34523. These vulnerabilities, known as ProxyShell, affect Microsoft Exchange email servers. In combination, successful exploitation enables a remote actor to execute arbitrary code. These vulnerabilities reside within the Microsoft Client Access Service (CAS), which typically runs on port 443 in Microsoft Internet Information Services (IIS) (e.g., Microsoft’s web server). CAS is commonly exposed to the internet to enable users to access their email via mobile devices and web browsers.
• CVE-2021-40539. This vulnerability enables unauthenticated remote code execution (RCE) in Zoho ManageEngine ADSelfService Plus and was linked to the usage of an outdated third-party dependency. Initial exploitation of this vulnerability began in late 2021 and continued throughout 2022.
• CVE-2021-26084. This vulnerability, affecting Atlassian Confluence Server and Data Center (a web-based collaboration tool used by governments and private companies) could enable an unauthenticated cyber actor to execute arbitrary code on vulnerable systems. This vulnerability quickly became one of the most routinely exploited vulnerabilities after a PoC was released within a week of its disclosure. Attempted mass exploitation of this vulnerability was observed in September 2021.
• CVE-2021- 44228. This vulnerability, known as Log4Shell, affects Apache’s Log4j library, an open-source logging framework incorporated into thousands of products worldwide. An actor can exploit this vulnerability by submitting a specially crafted request to a vulnerable system, causing the execution of arbitrary code. The request allows a cyber actor to take full control of a system. The actor can then steal information, launch ransomware, or conduct other malicious activity.[1] Malicious cyber actors began exploiting the vulnerability after it was publicly disclosed in December 2021, and continued to show high interest in CVE-2021- 44228 through the first half of 2022.
• CVE-2022-22954, CVE-2022-22960. These vulnerabilities allow RCE, privilege escalation, and authentication bypass in VMware Workspace ONE Access, Identity Manager, and other VMware products. A malicious cyber actor with network access could trigger a server-side template injection that may result in remote code execution. Exploitation of CVE-2022-22954 and CVE-2022-22960 began in early 2022 and attempts continued throughout the remainder of the year.
• CVE-2022-1388. This vulnerability allows unauthenticated malicious cyber actors to bypass iControl REST authentication on F5 BIG-IP application delivery and security software.
• CVE-2022-30190. This vulnerability impacts the Microsoft Support Diagnostic Tool (MSDT) in Windows. A remote, unauthenticated cyber actor could exploit this vulnerability to take control of an affected system.
• CVE-2022-26134. This critical RCE vulnerability affects Atlassian Confluence and Data Center. The vulnerability, which was likely initially exploited as a zero-day before public disclosure in June 2022, is related to an older Confluence vulnerability (CVE-2021-26084), which cyber actors also exploited in 2022.

Additional Routinely Exploited Vulnerabilities

In addition to the 12 vulnerabilities listed in Table 1, the authoring agencies identified vulnerabilities—listed in Table 2—that were also routinely exploited by malicious cyber actors in 2022.

MITIGATIONS

Vendors and Developers

The authoring agencies recommend vendors and developers take the following steps to ensure their products are secure by design and default:

• Identify repeatedly exploited classes of vulnerability. Perform an analysis of both CVEs and known exploited vulnerabilities to understand which classes of vulnerability are identified more than others. Implement appropriate mitigations to eliminate those classes of vulnerability. For example, if a product has several instances of SQL injection vulnerabilities, ensure all database queries in the product use parameterized queries, and prohibit other forms of queries.
• Ensure business leaders are responsible for security. Business leaders should ensure that proactive steps to eliminate entire classes of security vulnerabilities, rather than only making one-off patches when new vulnerabilities are discovered.
• Follow the SSDF (SP 800-218) and implement secure design practices into each stage of the SDLC. Pay attention to:
  • Prioritizing the use of memory safe languages wherever possible [SSDF PW 6.1].
  • Exercising due diligence when selecting software components (e.g., software libraries, modules, middleware, frameworks) to ensure robust security in consumer software products [SSDF PW 4.1].
  • Setting up secure development team practices; this includes conducting peer code reviews, working to a common organization secure coding standard, and maintaining awareness of language specific security concerns [SSDF PW.5.1, PW.7.1, PW.7.2].
  • Establishing a vulnerability disclosure program to verify and resolve security vulnerabilities disclosed by people who may be internal or external to the organization [SSDF RV.1.3]. As part of this, establish processes to determine root causes of discovered vulnerabilities.
  • Using static and dynamic application security testing (SAST/DAST) tools to analyze product source code and application behavior to detect error-prone practices [SSDF PW.7.2, PW.8.2].
  • Configuring production-ready products to have to most secure settings as default and providing guidance on the risks of changing each setting [SSDF PW.9.1, PW9.2]
• Prioritize secure-by-default configurations such as eliminating default passwords, implementing single sign on (SSO) technology via modern open standards, and providing high-quality audit logs to customers with no additional configuration and at no extra charge.
• Ensure published CVEs include the proper CWE field identifying the root cause of the vulnerability to enable industry-wide analysis of software security and design flaws.

For more information on designing secure-by-design and -default products, including additional recommended secure-by-default configurations, see joint guide Shifting the Balance of Cybersecurity Risk: Principles and Approaches for Security-by-Design and -Default.

End-User Organizations

The authoring agencies recommend end-user organizations implement the mitigations below to improve cybersecurity posture on the basis of the threat actors’ activity. These mitigations align with the cross-sector Cybersecurity Performance Goals (CPGs) developed by CISA and the National Institute of Standards and Technology (NIST). The CPGs provide a minimum set of practices and protections that CISA and NIST recommend all organizations implement. CISA and NIST based the CPGs on existing cybersecurity frameworks and guidance to protect against the most common and impactful threats, tactics, techniques, and procedures. Visit CISA’s Cross-Sector Cybersecurity Performance Goals for more information on CPGs, including additional recommended baseline protections.

Vulnerability and Configuration Management

• Update software, operating systems, applications, and firmware on IT network assets in a timely manner [CPG 1.E]. Prioritize patching known exploited vulnerabilities, especially those CVEs identified in this CSA, then critical and high vulnerabilities that allow for remote code execution or denial-of-service on internet-facing equipment. For patch information on CVEs identified in this CSA, refer to the appendix.
  • If a patch for a known exploited or critical vulnerability cannot be quickly applied, implement vendor-approved workarounds.
  • Replace end-of-life software (i.e., software no longer supported by the vendor).
• Routinely perform automated asset discovery across the entire estate to identify and catalogue all the systems, services, hardware and software.
• Implement a robust patch management process and centralized patch management system that establishes prioritization of patch applications [CPG 1.A].
  • Organizations that are unable to perform rapid scanning and patching of internet-facing systems should consider moving these services to mature, reputable cloud service providers (CSPs) or other managed service providers (MSPs). Reputable MSPs can patch applications—such as webmail, file storage, file sharing, and chat and other employee collaboration tools—for their customers. However, MSPs and CSPs can expand their customer’s attack surface and may introduce unanticipated risks, so organizations should proactively collaborate with their MSPs and CSPs to jointly reduce risk [CPG 1.F]. For more information and guidance, see the following resources.
• Document secure baseline configurations for all IT/OT components, including cloud infrastructure. Monitor, examine, and document any deviations from the initial secure baseline [CPG 2.O].
• Perform regular secure system backups and create known good copies of all device configurations for repairs and/or restoration. Store copies off-network in physically secure locations and test regularly [CPG 2.R].
• Maintain an updated cybersecurity incident response plan that is tested at least annually and updated within a risk informed time frame to ensure its effectiveness [CPG 2.S].

Identity and Access Management

• Enforce phishing-resistant multifactor authentication (MFA) for all users, without exception. [CPG 2.H].
• Enforce MFA on all VPN connections. If MFA is unavailable, require employees engaging in remote work to use strong passwords [CPG 2.A, 2.B, 2.C, 2.D, 2.G].
• Regularly review, validate, or remove privileged accounts (annually at a minimum) [CPG 2.D, 2.E].
• Configure access control under the principle of least privilege [CPG 2.Q].

Protective Controls and Architecture

• Properly configure and secure internet-facing network devices, disable unused or unnecessary network ports and protocols, encrypt network traffic, and disable unused network services and devices [CPG 2.V, 2.W, 2X].
  • Harden commonly exploited enterprise network services, including Link-Local Multicast Name Resolution (LLMNR) protocol, Remote Desktop Protocol (RDP), Common Internet File System (CIFS), Active Directory, and OpenLDAP.
  • Manage Windows Key Distribution Center (KDC) accounts (e.g., KRBTGT) to minimize Golden Ticket attacks and Kerberoasting.
  • Strictly control the use of native scripting applications, such as command-line, PowerShell, WinRM, Windows Management Instrumentation (WMI), and Distributed Component Object Model (DCOM).

• Implement Zero Trust Network Architecture (ZTNA) to limit or block lateral movement by controlling access to applications, devices, and databases. Use private virtual local area networks [CPG 2.F, 2.X]. Note: See the Department of Defense’s Zero Trust Reference Architecture for additional information on Zero Trust.
• Continuously monitor the attack surface and investigate abnormal activity that may indicate cyber actor or malware lateral movement [CPG 2.T].
  • Use security tools, such as endpoint detection and response (EDR) and security information and event management (SIEM) tools. Consider using an information technology asset management (ITAM) solution to ensure EDR, SIEM, vulnerability scanner, and other similar tools are reporting the same number of assets [CPG 2.T, 2.V].
  • Use web application firewalls to monitor and filter web traffic. These tools are commercially available via hardware, software, and cloud-based solutions, and may detect and mitigate exploitation attempts where a cyber actor sends a malicious web request to an unpatched device [CPG 2.B, 2.F].
  • Implement an administrative policy and/or automated process configured to monitor unwanted hardware, software, or programs against an allowlist with specified approved versions [CPG 2.Q].
  • Use a network protocol analyzer to examine captured data, including packet-level data.

Supply Chain Security

• Reduce third-party applications and unique system/application builds—provide exceptions only if required to support business critical functions [CPG 2.Q].
• Ensure contracts require vendors and/or third-party service providers to:
  • Provide notification of security incidents and vulnerabilities within a risk informed time frame [CPG 1.G, 1.H, 1.I].
  • Supply a Software Bill of Materials (SBOM) with all products to enhance vulnerability monitoring and to help reduce time to respond to identified vulnerabilities [CPG 4.B].
• Ask your software providers to discuss their secure by design program and to provide links to information about how they are working to remove classes of vulnerabilities, and to set secure default settings.

RESOURCES

• For information on the top vulnerabilities routinely exploited in 2016 through 2019, 2020, and 2021, see:
• See the appendix for additional partner resources on the vulnerabilities mentioned in this CSA.
• See ACSC’s Essential Eight mitigation strategies for additional mitigations.
• See ACSC’s Cyber Supply Chain Risk Management for additional considerations and advice.

DISCLAIMER

The information in this report is being provided “as is” for informational purposes only. CISA, FBI, NSA, ACSC, CCCS, NCSC-NZ, CERT NZ, and NCSC-UK do not endorse any commercial product or service, including any subjects of analysis. Any reference to specific commercial products, processes, or services by service mark, trademark, manufacturer, or otherwise, does not constitute or imply endorsement, recommendation, or favoring.

PURPOSE

This document was developed by CISA, NSA, FBI, ACSC, CCCS, NCSC-NZ, CERT NZ, and NCSC-UK in furtherance of their respective cybersecurity missions, including their responsibilities to develop and issue cybersecurity specifications and mitigations.

REFERENCES

[1] Apache Log4j Vulnerability Guidance

VERSION HISTORY

August 3, 2023: Initial version.

APPENDIX: PATCH INFORMATION AND ADDITIONAL RESOURCES FOR TOP EXPLOITED VULNERABILITIES

This joint Cybersecurity Advisory (CSA) was coauthored by cybersecurity authorities of the United States, Australia, Canada, New Zealand, and the United Kingdom: the Cybersecurity and Infrastructure Security Agency (CISA), National Security Agency (NSA), Federal Bureau of Investigation (FBI), Australian Cyber Security Centre (ACSC), Canadian Centre for Cyber Security (CCCS), New Zealand National Cyber Security Centre (NZ NCSC), and United Kingdom’s National Cyber Security Centre (NCSC-UK). This advisory provides details on the top 15 Common Vulnerabilities and Exposures (CVEs) routinely exploited by malicious cyber actors in 2021, as well as other CVEs frequently exploited.

U.S., Australian, Canadian, New Zealand, and UK cybersecurity authorities assess, in 2021, malicious cyber actors aggressively targeted newly disclosed critical software vulnerabilities against broad target sets, including public and private sector organizations worldwide. To a lesser extent, malicious cyber actors continued to exploit publicly known, dated software vulnerabilities across a broad spectrum of targets. 

The cybersecurity authorities encourage organizations to apply the recommendations in the Mitigations section of this CSA. These mitigations include applying timely patches to systems and implementing a centralized patch management system to reduce the risk of compromise by malicious cyber actors.

Click here for a PDF version of this report. 

Key Findings

Globally, in 2021, malicious cyber actors targeted internet-facing systems, such as email servers and virtual private network (VPN) servers, with exploits of newly disclosed vulnerabilities. For most of the top exploited vulnerabilities, researchers or other actors released proof of concept (POC) code within two weeks of the vulnerability’s disclosure, likely facilitating exploitation by a broader range of malicious actors.

To a lesser extent, malicious cyber actors continued to exploit publicly known, dated software vulnerabilities—some of which were also routinely exploited in 2020 or earlier. The exploitation of older vulnerabilities demonstrates the continued risk to organizations that fail to patch software in a timely manner or are using software that is no longer supported by a vendor.

Top 15 Routinely Exploited Vulnerabilities

Table 1 shows the top 15 vulnerabilities U.S., Australian, Canadian, New Zealand, and UK cybersecurity authorities observed malicious actors routinely exploiting in 2021, which include:

• CVE-2021-44228. This vulnerability, known as Log4Shell, affects Apache’s Log4j library, an open-source logging framework. An actor can exploit this vulnerability by submitting a specially crafted request to a vulnerable system that causes that system to execute arbitrary code. The request allows a cyber actor to take full control over the system. The actor can then steal information, launch ransomware, or conduct other malicious activity.[1] Log4j is incorporated into thousands of products worldwide. This vulnerability was disclosed in December 2021; the rapid widespread exploitation of this vulnerability demonstrates the ability of malicious actors to quickly weaponize known vulnerabilities and target organizations before they patch.
• CVE-2021-26855, CVE-2021-26858, CVE-2021-26857, CVE-2021-27065. These vulnerabilities, known as ProxyLogon, affect Microsoft Exchange email servers. Successful exploitation of these vulnerabilities in combination (i.e., “vulnerability chaining”) allows an unauthenticated cyber actor to execute arbitrary code on vulnerable Exchange Servers, which, in turn, enables the actor to gain persistent access to files and mailboxes on the servers, as well as to credentials stored on the servers. Successful exploitation may additionally enable the cyber actor to compromise trust and identity in a vulnerable network.
• CVE-2021-34523, CVE-2021-34473, CVE-2021-31207. These vulnerabilities, known as ProxyShell, also affect Microsoft Exchange email servers. Successful exploitation of these vulnerabilities in combination enables a remote actor to execute arbitrary code. These vulnerabilities reside within the Microsoft Client Access Service (CAS), which typically runs on port 443 in Microsoft Internet Information Services (IIS) (e.g., Microsoft’s web server). CAS is commonly exposed to the internet to enable users to access their email via mobile devices and web browsers. 
• CVE-2021-26084. This vulnerability, affecting Atlassian Confluence Server and Data Center, could enable an unauthenticated actor to execute arbitrary code on vulnerable systems. This vulnerability quickly became one of the most routinely exploited vulnerabilities after a POC was released within a week of its disclosure. Attempted mass exploitation of this vulnerability was observed in September 2021.

Three of the top 15 routinely exploited vulnerabilities were also routinely exploited in 2020: CVE-2020-1472, CVE-2018-13379, and CVE-2019-11510. Their continued exploitation indicates that many organizations fail to patch software in a timely manner and remain vulnerable to malicious cyber actors.

Table 1: Top 15 Routinely Exploited Vulnerabilities in 2021

Additional Routinely Exploited Vulnerabilities

In addition to the 15 vulnerabilities listed in table 1, U.S., Australian, Canadian, New Zealand, and UK cybersecurity authorities identified vulnerabilities, listed in table 2, that were also routinely exploited by malicious cyber actors in 2021. 

These vulnerabilities include multiple vulnerabilities affecting internet-facing systems, including Accellion File Transfer Appliance (FTA), Windows Print Spooler, and Pulse Secure Pulse Connect Secure. Three of these vulnerabilities were also routinely exploited in 2020: CVE-2019-19781, CVE-2019-18935, and CVE-2017-11882.

Table 2: Additional Routinely Exploited Vulnerabilities in 2021

Vulnerability and Configuration Management

• Update software, operating systems, applications, and firmware on IT network assets in a timely manner. Prioritize patching known exploited vulnerabilities, especially those CVEs identified in this CSA, and then critical and high vulnerabilities that allow for remote code execution or denial-of-service on internet-facing equipment. For patch information on CVEs identified in this CSA, refer to the appendix. 
  • If a patch for a known exploited or critical vulnerability cannot be quickly applied, implement vendor-approved workarounds.
• Use a centralized patch management system.
• Replace end-of-life software, i.e., software that is no longer supported by the vendor. For example, Accellion FTA was retired in April 2021.
• Organizations that are unable to perform rapid scanning and patching of internet-facing systems should consider moving these services to mature, reputable cloud service providers (CSPs) or other managed service providers (MSPs). Reputable MSPs can patch applications—such as webmail, file storage, file sharing, and chat and other employee collaboration tools—for their customers. However, as MSPs and CSPs expand their client organization’s attack surface and may introduce unanticipated risks, organizations should proactively collaborate with their MSPs and CSPs to jointly reduce that risk. For more information and guidance, see the following resources.

Identity and Access Management

• Enforce multifactor authentication (MFA) for all users, without exception.
• Enforce MFA on all VPN connections. If MFA is unavailable, require employees engaging in remote work to use strong passwords. 
• Regularly review, validate, or remove privileged accounts (annually at a minimum).
• Configure access control under the concept of least privilege principle.
  • Ensure software service accounts only provide necessary permissions (least privilege) to perform intended functions (non-administrative privileges).

Note: see CISA Capacity Enhancement Guide – Implementing Strong Authentication and ACSC guidance on Implementing Multi-Factor Authentication for more information on hardening authentication systems.

Protective Controls and Architecture 

• Properly configure and secure internet-facing network devices, disable unused or unnecessary network ports and protocols, encrypt network traffic, and disable unused network services and devices. 
  • Harden commonly exploited enterprise network services, including Link-Local Multicast Name Resolution (LLMNR) protocol, Remote Desktop Protocol (RDP), Common Internet File System (CIFS), Active Directory, and OpenLDAP.
  • Manage Windows Key Distribution Center (KDC) accounts (e.g., KRBTGT) to minimize Golden Ticket attacks and Kerberoasting.
  • Strictly control the use of native scripting applications, such as command-line, PowerShell, WinRM, Windows Management Instrumentation (WMI), and Distributed Component Object Model (DCOM).
• Segment networks to limit or block lateral movement by controlling access to applications, devices, and databases. Use private virtual local area networks. 
• Continuously monitor the attack surface and investigate abnormal activity that may indicate lateral movement of a threat actor or malware.
  • Use security tools, such as endpoint detection and response (EDR) and security information and event management (SIEM) tools. Consider using an information technology asset management (ITAM) solution to ensure your EDR, SIEM, vulnerability scanner etc., are reporting the same number of assets.
  • Monitor the environment for potentially unwanted programs.
• Reduce third-party applications and unique system/application builds; provide exceptions only if required to support business critical functions.
• Implement application allowlisting. 

Resources

Disclaimer

The information in this report is being provided “as is” for informational purposes only. CISA, the FBI, NSA, ACSC, CCCS, NZ NCSC, and NCSC-UK do not endorse any commercial product or service, including any subjects of analysis. Any reference to specific commercial products, processes, or services by service mark, trademark, manufacturer, or otherwise, does not constitute or imply endorsement, recommendation, or favoring.

Purpose 

This document was developed by U.S., Australian, Canadian, New Zealand, and UK cybersecurity authorities in furtherance of their respective cybersecurity missions, including their responsibilities to develop and issue cybersecurity specifications and mitigations.

References

[1] CISA’s Apache Log4j Vulnerability Guidance

Appendix: Patch Information and Additional Resources for  Top Exploited Vulnerabilities