Threat Signal Report

New Log4j Vulnerability (CVE-2021-45046) Results in Denial of Service

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UPDATE December 17 2021: The Apache Software Foundation has changed Denial of Service to Remote Code Execution and has upgraded a CVSS score from 3.7 to 9.0 as such this Threat Signal has been updated accordingly along with protection information.

What is the Vulnerability? (Updated on December 17th)

This is a new vulnerability (CVE-2021-45046) discovered in Log4j, the same utility that last week announced a critical vulnerability known as Log4Shell (CVE-2021-44228). Successfully exploiting this new vulnerability would result in an information leak and remote code execution (RCE) in some environments and local code execution in all environments. Initially CVE-2021-45046 was identified as a Denial of Service vulnerability.

The new vulnerability is tracked as CVE-2021-45046. The vulnerability was initially given a CVSS score of 3.7, however the score was upgraded to 9.0 as remote code execution and information leak could be achieved as a result of successful exploitation.

Apache provides the following updated description in their advisory on December 16th:

It was found that the fix to address CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. When the logging configuration uses a non-default Pattern Layout with a Context Lookup (for example, $${ctx:loginId}), attackers with control over Thread Context Map (MDC) input data can craft malicious input data using a JNDI Lookup pattern, resulting in an information leak and remote code execution in some environments and local code execution in all environments; remote code execution has been demonstrated on macOS but no other tested environments.

FortiGuard Labs previously released Threat Signal for CVE-2021-44228 (Log4Shell). See the Appendix for a link to "Apache Log4J Remote Code Execution Vulnerability (CVE-2021-44228)".

What Versions of Log4j are Affected?

All versions from 2.0-beta9 through 2.12.1 and 2.13.0 through 2.15.0

Has Apache Released a Fix for CVE-2021-45046?

Yes. In response to the issue, Apache Log4j 2.16.0 was released for Java 8 and up and 2.12.2 for Java 7.

What is the Status of Coverage? (Updated on December 17th)

FortiGuard Labs provides the following AV coverage against CVE-2021-45046:


Any Suggested Mitigation?

Apache provides the following mitigation in their advisory:

Log4j 1.x mitigation: Log4j 1.x is not impacted by this vulnerability.

Log4j 2.x mitigation: Implement one of the mitigation techniques below.

Java 8 (or later) users should upgrade to release 2.16.0.

Users requiring Java 7 should upgrade to release 2.12.2 when it becomes available (work in progress, expected to be available soon).

Otherwise, remove the JndiLookup class from the classpath: zip -q -d log4j-core-*.jar org/apache/logging/log4j/core/lookup/JndiLookup.class

Note that only the log4j-core JAR file is impacted by this vulnerability. Applications using only the log4j-api JAR file without the log4j-core JAR file are not impacted by this vulnerability.



Traffic Light Protocol

Color When Should it Be used? How may it be shared?


Not for disclosure, restricted to participants only.
Sources may use TLP:RED when information cannot be effectively acted upon by additional parties, and could lead to impacts on a party's privacy, reputation, or operations if misused. Recipients may not share TLP:RED information with any parties outside of the specific exchange, meeting, or conversation in which it was originally disclosed. In the context of a meeting, for example, TLP:RED information is limited to those present at the meeting. In most circumstances, TLP:RED should be exchanged verbally or in person.


Limited disclosure, restricted to participants’ organizations.
Sources may use TLP:AMBER when information requires support to be effectively acted upon, yet carries risks to privacy, reputation, or operations if shared outside of the organizations involved. Recipients may only share TLP:AMBER information with members of their own organization, and with clients or customers who need to know the information to protect themselves or prevent further harm. Sources are at liberty to specify additional intended limits of the sharing: these must be adhered to.


Limited disclosure, restricted to the community.
Sources may use TLP:GREEN when information is useful for the awareness of all participating organizations as well as with peers within the broader community or sector. Recipients may share TLP:GREEN information with peers and partner organizations within their sector or community, but not via publicly accessible channels. Information in this category can be circulated widely within a particular community. TLP:GREEN information may not be released outside of the community.


Disclosure is not limited.
Sources may use TLP:WHITE when information carries minimal or no foreseeable risk of misuse, in accordance with applicable rules and procedures for public release. Subject to standard copyright rules, TLP:WHITE information may be distributed without restriction.