Detecting Apache Text4Shell (CVE-2022-42889) with Wazuh

| by Pacome Kemkeu | Wazuh 4.3
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A vulnerability in the Apache Commons Text library called Text4Shell was discovered in October 2022. This vulnerability exists in versions 1.5 through 1.9 of the popular Java library. It allows remote code execution and other malicious actions through the exploitation of the StringSubstitutor API. The vulnerability is identified as CVE-2022-42889 and has a CVSSv3 score of 9.8 out of 10. 

The Apache Commons Text library includes a mechanism for interpolating variables, allowing users to replace certain bits of text with another according to a template. The default template for this library is ${prefix:[options]:data}, where the prefix defines the algorithm for processing data from options.

In this blog post, we use Wazuh to detect vulnerable versions of Apache Commons Text Library and monitor the endpoints for attempts to exploit this vulnerability.

Exploitation conditions​ for Text4Shell

The following conditions must be met for Text4Shell to be exploitable:

  • Apache Commons Text version 1.5 through 1.9 installed on the victim endpoint.
  • The application using the vulnerable library must use org.apache.commons.text.StringSubstitutor and one of the following prefixes with the default configuration (dns, script, url). 
  • The application must accept and process untrusted data input.

Exploitation examples

If an attacker has the ability to modify a template, he can carry out the following types of attacks:

AttackPrefixExamples
Remote code executionscript${script:javascript:java.lang.Runtime.getRuntime().exec(‘touch /tmp/foo’)}
${script:JEXL:”.getClass().forName(‘java.lang.Runtime’).getRuntime().exec(‘touch /tmp/pwned’)}
Sending information through DNS queries to malicious domains.dns${dns:address|commons.apache.org}
Disclosure of internal network information via HTTP (HTTPS) requestsurl${url:UTF-8:https://nvd.nist.gov/vuln/detail/CVE-2022-42889}

Detection with Wazuh

Requirements

1. A pre-built ready-to-use Wazuh OVA 4.3.10 Follow this guide to download the virtual machine.

2. An Ubuntu 22.04 endpoint with a Wazuh agent installed and enrolled to the Wazuh server. A Wazuh agent can be installed by following the Deploying Wazuh agents guide.

Ubuntu 22.04 endpoint

In order to test the Text4shell vulnerability, we used the vulnerable application in this Proof of Concept.

1. Install OpenJDK and Maven:

$ sudo apt update && sudo apt install openjdk-11-jdk
$ cd /tmp
$ sudo wget https://mirrors.estointernet.in/apache/maven/maven-3/3.6.3/binaries/apache-maven-3.6.3-bin.tar.gz
$ sudo tar -xvf apache-maven-3.6.3-bin.tar.gz
$ sudo mv apache-maven-3.6.3 /opt/

2. Set the environment parameters for Maven:

$ M2_HOME='/opt/apache-maven-3.6.3'
$ PATH="$M2_HOME/bin:$PATH"
$ export PATH

3. Download and build the vulnerable application:

$ sudo apt install git
$ sudo git clone https://github.com/securekomodo/text4shell-poc.git
$ cd text4shell-poc
$ sudo ./mvnw clean install

This creates the ./target folder in the current working directory. Within that folder is the JAR file text4shell-poc-0.0.1-SNAPSHOT.jar

4. Deploy the vulnerable application and enable logging:

$ sudo java -jar -Dserver.tomcat.basedir=tomcat -Dserver.tomcat.accesslog.enabled=true ./target/text4shell-poc-0.0.1-SNAPSHOT.jar

5. In a new terminal, forward the application logs to the Wazuh server by editing the agent /var/ossec/etc/ossec.conf configuration file and specifying the path to the log file:

<localfile>
  <log_format>syslog</log_format>
  <location>/path/to/tomcat/access_log.x-x-x.log</location>
</localfile>

This file is under tomcat/logs in the current working directory for this use case.

Detecting vulnerable versions of Apache Commons Text library with Wazuh SCA

The Wazuh SCA module performs scans to discover misconfigurations in monitored endpoints. Policy files are written in YAML and contain rules to be tested against the actual configuration of the endpoint.

Ubuntu endpoint

1. Create a directory on the endpoint to hold local SCA policies:

$ sudo mkdir /home/local_sca_policies/

The custom SCA policies in the Wazuh default ruleset folders are not kept across updates. This is why we create the /home/local_sca_policies/ directory outside the Wazuh agent installation folder.

2. Create the text4shell_policy.yml file in the local SCA policy directory on the endpoint:

$ sudo touch /home/local_sca_policies/text4shell_policy.yml

3. Change the owner and group of the policy file to wazuh:wazuh so that it can be used by the Wazuh user:

$ sudo chown wazuh:wazuh /home/local_sca_policies/text4shell_policy.yml

4. Enable the policy in the Wazuh agent configuration file /var/ossec/etc/ossec.conf by specifying the location of the policy file in the <SCA> block:

<policies>
   <policy>/home/local_sca_policies/text4shell_policy.yml</policy>
</policies>

5. Add the following content in your /home/local_sca_policies/text4shell_policy.yml policy file:

policy:
 id: "text4shell_check"
 file: "text4shell_check.yml"
 name: "Text4Shell dependency check"
 description: "This document provides prescriptive guidance for identifying Text4shell vulnerability"
 references:
   - https://nvd.nist.gov/vuln/detail/CVE-2022-42889
   - https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-42889
requirements:
 title: "Check if Java is present on the machine"
 description: "Requirements for running the SCA scan against machines with Java on them."
 condition: none
 Rules:
   - 'c:sh -c "java -version" -> r: not found'
checks:
 - id: 10000
   title: "Ensure Apache Commons Text earlier than v1.10 is not on the system"
   description: "The Apache Commons Text library is vulnerable to RCE on versions between 1.5 to 1.9."
   remediation: "Update the Apache Commons Text library to version 1.10."
   condition: none
   rules:
     - 'c:find / -regex ".*commons-text.*.jar" -type f -exec sh -c "unzip -p {} META-INF/MANIFEST.MF | grep Implementation-Version" \; -> r: 1.5| 1.6| 1.7| 1.8| 1.9'

The check 10000 searches for vulnerable versions of  Apache Commons Text library on the endpoint. This SCA check will fail if a vulnerable version is found.

6. Restart the Wazuh agent to apply the changes:

$ sudo systemctl restart wazuh-agent

Detection results

We can confirm from the SCA dashboard that the endpoint currently has a vulnerable version of the Apache Commons Text Library installed.

text4shell
Figure 1: Text4Shell SCA detection results

Note

To implement this SCA policy across a group of agents, refer to the SCA section of Wazuh documentation.

Detecting Apache Text4Shell exploitation attempts

In order to detect the exploitation of this vulnerability, we write a rule that can match different exploit strings encoded in web requests.

Wazuh server

1. Edit the /var/ossec/etc/rules/local_rules.xml file and add the following custom rules: 

<group name="accesslog,text4shell,">

<!-- This rule matches arbitrary controlled input for exploitation using script, dns or url prefixes -->

  <rule id="100002" level="12">
     <if_sid>31100</if_sid>
     <url type="pcre2">%24%7B(script%3A(javascript|JEXL)%3A|url%3AUTF-8%3A|dns%3A(address|canonical-name|name)%7C)</url>
     <description>Possible Text4Shell (CVE-2022-42889) exploitation attempt detected from $(srcip)</description>
     <mitre>
      <id>T1190</id>
      <id>T1203</id>
     <id>T1210</id>
   </mitre>
  </rule>

</group>

2. Restart the Wazuh manager to apply the changes:

# systemctl restart wazuh-manager

Attack Emulation

To test the detection, send the following web requests to the vulnerable application from any device that has network connectivity with the endpoint:

1. Using the script prefix:

$ curl http://<UBUNTU_IP>:8080/reflected?poc=%24%7Bscript%3Ajavascript%3Ajava.lang.Runtime.getRuntime%28%29.exec%28%27touch%20%2Ftmp%2Ffoo%27%29%7D

This request allows the supplied JavaScript code to be executed. This example creates a file named foo in the /tmp directory of the monitored endpoint.

2. Using the DNS prefix:

$ curl http://<UBUNTU_IP>:8080/reflected?poc=%24%7Bdns%3Aaddress%7Cwww.google.com%7D

This request performs a DNS query, or a reverse lookup to identify internal resources. 

3. Using the URL prefix:

$ curl http://<UBUNTU_IP>:8080/reflected?poc=%24%7Burl%3AUTF-8%3Ahttps%3A%2F%2Fnvd.nist.gov%2Fvuln%2Fdetail%2FCVE-2022-42889%7D

This lookup calls the specified URL to perform basic GET requests to internal resources.

Replace <UBUNTU_IP> with the IP address of the monitored endpoint running the vulnerable application.

Detection results

text4shell with wazuh
Figure 2: Text4Shell exploitation alerts on Wazuh dashboard
detecting apache text4shell
Figure 3: Text4Shell exploitation details on Wazuh dashboard

Mitigations

Apache has released a patch for this vulnerability. Upgrading the Apache Commons Text Library version to 1.10 mitigates the vulnerability. Additionally, check the usage of org.apache.commons.text.StringSubstitutor closely across your codebase and ensure untrusted user input isn’t being passed to vulnerable functions.

Conclusion

In this article, we demonstrate how to detect Text4shell vulnerability by monitoring an endpoint for vulnerable versions of Apache Commons Text Library. To achieve this, we used the Wazuh SCA module and wrote custom rules to detect exploitation attempts on the monitored endpoint.

Wazuh is open source and free to use. It also has a fast-growing community. You can deploy Wazuh on-premises or as a cloud solution using the Wazuh cloud.

References