[BUG] ClassLoader Leak in AesGcmEncryption due to uncleaned ThreadLocal

[QiuYucheng2003]

Description:

Summary
The AesGcmEncryption class uses a ThreadLocal to cache encryption handles. In Web container environments (e.g., Tomcat), this leads to ClassLoader Pinning because the Cipher object, loaded by the WebappClassLoader, is strongly referenced by long-lived container threads.

Technical Details
Vulnerable Field: private ThreadLocal cipherWrapper.

Mechanism: When getCipher() is called, a Cipher instance is bound to the current thread's ThreadLocalMap.

The Leak: There is no cipherWrapper.remove() call in the codebase. This creates a reference chain: Thread -> ThreadLocalMap -> Cipher -> WebappClassLoader, preventing the application from being fully undeployed.

Impact
Repeated hot redeployments will cause Metaspace/PermGen exhaustion (OOM), requiring a full JVM restart to recover.

Suggested Fix

1. Remove ThreadLocal: Modern JVMs handle Cipher.getInstance() efficiently; caching may not be necessary.

2. Explicit Cleanup: If caching is required, implement a cleanup mechanism (e.g., a destroy() method) that invokes cipherWrapper.remove() on active threads.