---
title: "Java 21 Upgrade & Compatibility Analysis: Log4j 1.2.17 vs. Jackson Annotations 2.17.2"
published: true
tags: java, maven, gradle, security
canonical_url:
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# Java 21 Upgrade & Compatibility Analysis
This guide breaks down the compatibility, security risks, JVM runtime flags, and migration strategies for **Log4j 1.2.17** and **Jackson Annotations 2.17.2** when running on **Java 21**.
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## 1. Artifact: `log4j:log4j:1.2.17`
### Overview & JDK Target
* **Original JDK Target:** Java 1.4 (Class file major/minor version `48.0`). Built to run on JDK 1.4 through JDK 8.
* **Java 21 Behavior:** When executing directly under Java 21 without upgrading, strong Java Platform Module System (JPMS) encapsulation blocks reflection into internal JDK APIs unless explicit command-line flags are configured.
### Critical Vulnerabilities & Security Risks
Log4j 1.2.17 has been **End-of-Life (EOL) since August 2015** and contains severe unpatched security vulnerabilities:
* **CVE-2019-17571 (CVSS 9.8):** Remote Code Execution (RCE) via untrusted deserialization in `SocketServer`.
* **CVE-2021-4104:** Deserialization vulnerability when configured to use `JMSAppender`.
* **CVE-2022-23302:** Deserialization vulnerability when configured to use `JMSSink`.
* **CVE-2022-23305 (CVSS 9.8):** SQL Injection in `JDBCAppender`.
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### Temporary Workaround: JVM Command-Line Flags
If you cannot immediately upgrade dependencies and must run unpatched `log4j:log4j:1.2.17` on Java 21, pass these JVM flags to bypass encapsulation restrictions:
bash
--add-opens=java.base/java.lang=ALL-UNNAMED
--add-opens=java.base/java.util=ALL-UNNAMED
-Dsun.util.logging.disableWindowWarning=true
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