CVE-2021-44228 - log4j Security Vulnerability#

11 Dec 2021, last updated 20 Dec 2021

Note: This advisory was updated on 20 Dec 2021 to provide an additional optional remediation step, as well as update regarding the newly discovered log4j vulnerability in CVE-2021-45105.

Note: This advisory was updated on 14 Dec 2021 to document the latest findings about log4j 1.2.17.

The log4j 2.x security issue disclosed in CVE-2021-44228 also affects some components of the Squirro Insight Engine. Squirro includes the following three Java services which all use log4j: Elasticsearch, Zooekeeper, Tika (embedded or as a separate server).

Issue identifier: CVE-2021-44228

Products and Versions: All versions of Squirro Insights Engine


Since OpenJDK 8u191 the vulnerability seems to not be exploitable (see e.g., Rapid7). The latest Squirro versions ship with the newer 1.8.0_312, and for at least the last three years Squirro has shipped Java runtimes higher than that version.

This document includes the configuration changes required to remediate the security problems. We will update this document when we release patches and version updates that fix the issue out of the box.

We are aware that some of our components (Tika and Zookeeper) include log4j 1.2.17. A separate CVE has been created for that version (CVE-2021-4104) and this version is only vulnerable if their configuration uses the JMSAppender. Squirro’s out-of-the-box configuration does not include this appender anywhere. As a result no immediate action is required for these components.

Update 20 Dec 2021 : On December 16th, 2021, CVE-2021-45105 was disclosed. It describes a Denial of Services vulnerability of the log4j framework. Elasticsearch has updated its guidance and declares Elasticsearch to be not vulnerable to this issue and that the mitigations outlined below are sufficient.


The official CVE communication recommends setting the system property log4j2.formatMsgNoLookups=true. Additionally you should check the JDK version.


Change Elasticsearch configuration by adding the following line to /etc/elasticsearch/jvm.options:


Apply the changes by running:

systemctl restart elasticsearch

As an optional, secondary mitigation, the affected JndiLookup.class file can easily be removed from the package. This hotfix works for all versions of Elasticsearch.

Take a backup of the jar file, to enable a rollback option:

tar -czf /usr/share/elasticsearch/log4j-hotfix-backup.tar.gz /usr/share/elasticsearch/lib/log4j-core-2.*

Install the zip utility if required and remove the affected JndiLookup.class class file from the jar file (jar files are actually zip files).

yum install -y zip
zip -q -d /usr/share/elasticsearch/lib/log4j-core-2.* org/apache/logging/log4j/core/lookup/JndiLookup.class

Apply the changes by running:

systemctl restart elasticsearch

Tika Service#

This is an optional component and is usually not yet installed. If the following file does not exist, you can safely assume that the Tika server has not been installed.

Adjust the ExecStart line in /usr/lib/systemd/system/tika.service and change it to include. -Dlog4j2.formatMsgNoLookups=true`. Depending on your Squirro version, this will change the line to:

ExecStart=/usr/bin/java -Dlog4j2.formatMsgNoLookups=true -jar /usr/share/java/tika-server.jar


ExecStart=/usr/bin/java -Dlog4j2.formatMsgNoLookups=true -jar /usr/share/java/tika-server.jar --includeStack -c /etc/tika-config.xml

Apply the changes by running the following two commands:

systemctl daemon-reload
systemctl restart tika


Check the JDK version with the following command:

java -version

If the version given is 1.8.0_121 or newer, the vulnerability should not be exploitable.

Web Application Firewall - WAF#

If you have deployed a WAF in your environment, check with your vendor if they already include detection rules for this vulnerability. It may be worth including those rules as well for additional protection.


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