Inside the Log4j2 vulnerability (CVE-2021-44228)
In 2013, in version 2.0-beta9, the Log4j package added the “JNDILookup plugin” in issue LOG4J2-313. To understand how that change creates a problem, it’s necessary to understand a little about JNDI: Java Naming and Directory Interface.
JNDI has been present in Java since the late 1990s. It is a directory service that allows a Java program to find data (in the form of a Java object) through a directory. JNDI has a number of service provider interfaces (SPIs) that enable it to use a variety of directory services. For example, SPIs exist for the CORBA COS (Common Object Service), the Java RMI (Remote Method Interface) Registry and LDAP. LDAP is a very popular directory service (the Lightweight Directory Access Protocol) and is the primary focus of CVE-2021-44228 (although other SPIs could potentially also be used).