This is a significant upgrade across many minor versions, introducing several breaking changes and important behavioral modifications.

Highlights:

• Java Version Requirement: Log4j version 2.17.2 and later require Java 8. The last version to support Java 7 was 2.12.4. [3]
• Security Hardening: Following the Log4Shell vulnerability, JNDI lookups are now disabled by default, and message pattern lookups have been restricted. [6] Applications relying on the previous, insecure behavior will break.
• Dependency Changes: The SLF4J binding is now split into two artifacts (log4j-slf4j-impl for SLF4J 1.7.x and log4j-slf4j18-impl for 1.8.x+). [3, 5] Additionally, some modules like log4j-mongodb3 and log4j-kubernetes have been removed and must be replaced. [5]

Source: Apache Log4j Release Notes
Recommendation: Verify your environment uses Java 8 or newer. Carefully review your configuration for any reliance on JNDI or message lookups. Update build dependencies to select the correct SLF4J binding and replace any removed modules.

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