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Apache Log4j Vulnerability Guidance

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Cyber Threats and Advisories

Summary

Note: CISA will continue to update this webpage as well as our community-sourced GitHub repository as we have further guidance to impart and additional vendor information to provide.

CISA and its partners, through the Joint Cyber Defense Collaborative, are responding to active, widespread exploitation of a critical remote code execution (RCE) vulnerability (CVE-2021-44228) in Apache’s Log4j software library, versions 2.0-beta9 to 2.14.1, known as "Log4Shell." Log4j is very broadly used in a variety of consumer and enterprise services, websites, and applications—as well as in operational technology products—to log security and performance information. An unauthenticated remote actor could exploit this vulnerability to take control of an affected system.

(Updated April 8, 2022) Organizations should continue identifying and remediating vulnerable Log4j instances within their environments and plan for long term vulnerability management. Consider the following in planning: 

  • Scope of covered assets: Due to the limited availability of initial information, identification and mitigation efforts may have been scoped to a limited number of an organization’s assets. For long term mitigation, ensure the prevalence of log4j in all assets is considered and accounted for, including internally developed software and non-internet facing technology stacks. 
  • Continuous enumeration and analysis: Organizations need to perform comprehensive analysis to fully enumerate all Log4J vulnerabilities. This should include scanning (network and host) and comparing installed software with software listed in CISA’s Log4j vulnerable software database.  
    • High fidelity scanning. Consider using file system scanning scripts to identify vulnerable Log4j files or use vulnerability scanners that leverage file scanning.  
    • Newly vulnerable 3rd party software. Organizations may lack insight into certain applications, such as Software as a Service (SaaS) solutions and other cloud resources. Organizations should continue to review the CISA log4j vulnerable software database and cross reference against used software. 
  • Patching over mitigation: If an update is available, it should be applied immediately. If a product cannot be updated, you should apply the temporary mitigation measures from the list at Mitigating Log4Shell and Other Log4j-Related Vulnerabilities. Note: while certain mitigation measures, such as removing the vulnerable class, can prevent exploitation, tracking each asset’s mitigation status adds administrative overhead so patching is preferred. If an asset cannot be patched or mitigated, consider removing it from the network. 

(Updated December 28, 2021) Organizations are urged to upgrade to Log4j 2.17.1 (Java 8), 2.12.4 (Java 7) and 2.3.2 (Java 6), and review and monitor the Apache Log4j Security Vulnerabilities webpage for updates and mitigation guidance. 

See CISA's joint Alert AA21-356A: Mitigating Log4Shell and Other Log4j-Related Vulnerabilities for more information. 

In order for vulnerabilities to be remediated in products and services that use affected versions of Log4j, the maintainers of those products and services must implement these security updates. Users of such products and services should refer to the vendors of these products/services for security updates. Given the severity of the vulnerabilities and the likelihood of an increase in exploitation by sophisticated cyber threat actors, CISA urges vendors and users to take the following actions. 

  • Vendors
    • Immediately identify, mitigate, and update affected products using Log4j to the latest version.

       
    • Inform your end users of products that contain these vulnerabilities and strongly urge them to prioritize software updates.

       
  • Affected Organizations

Technical Details

The CVE-2021-44228 RCE vulnerability—affecting Apache’s Log4j library, versions 2.0-beta9 to 2.14.1—exists in the action the Java Naming and Directory Interface (JNDI) takes to resolve variables. According to the CVE-2021-44228 listing, affected versions of Log4j contain JNDI features—such as message lookup substitution—that "do not protect against adversary-controlled LDAP [Lightweight Directory Access Protocol] and other JNDI related endpoints."

An adversary can exploit CVE-2021-44228 by submitting a specially crafted request to a vulnerable system that causes that system to execute arbitrary code. The request allows the adversary to take full control over the system. The adversary can then steal information, launch ransomware, or conduct other malicious activity. 

Actions for Organizations Running Products with Log4j

CISA recommends affected entities:

  • Review Apache’s Log4j Security Vulnerabilities page for additional information and, if appropriate, apply the provided workaround.
  • Apply available patches immediately.
    • Prioritize patching, starting with mission critical systems, internet-facing systems, and networked servers. Then prioritize patching other affected information technology and operational technology assets. 
    • As stated above, Emergency Directive (ED) 22-02: Mitigate Apache Log4j Vulnerability requires agencies to patch vulnerable internet-facing assets immediately.
  • Conduct a security review to determine if there is a security concern or compromise. The log files for any services using affected Log4j versions will contain user-controlled strings. 
  • Consider reporting compromises immediately to CISA and the FBI.

Resources

This information is provided “as-is” for informational purposes only. CISA does not endorse any company, product, or service referenced below.

Ongoing List of Impacted Products and Devices

CISA is maintaining a community-sourced GitHub repository that provides a list of publicly available information and vendor-supplied advisories regarding the Log4j vulnerability.

Ongoing Sources for Detection Rules 

CISA will update sources for detection rules as we obtain them.

For detection rules, see Florian Roth's GitHub page, log4j RCE Exploitation Detection. Note: due to the urgency to share this information, CISA has not yet validated this content.

For a list of hashes to help determine if a Java application is running a vulnerable version of Log4j, see Rob Fuller's GitHub page, CVE-2021-44228-Log4Shell-Hashes. Note: due to the urgency to share this information, CISA has not yet validated this content. 

Mitigation Guidance from JCDC Partners 

Additional Resources

 

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