Micronaut Framework is a JVM-based full stack Java framework designed for building modular, easily testable JVM applications. Prior to 4.10.22, the bundleCache is keyed by (Locale, baseName) where the locale originates from the HTTP Accept-Language header. In applications that explicitly register a ResourceBundleMessageSource bean and serve HTML error responses, an unauthenticated attacker can exhaust heap memory by sending requests with large numbers of unique Accept-Language values, each causing a new entry in the unbounded bundleCache. This vulnerability is fixed in 4.10.22.

Affected: Maven: io.micronaut:micronaut-inject

## Summary

`ResourceBundleMessageSource` maintains two caches: `messageCache` (bounded at 100 entries via `ConcurrentLinkedHashMap`) and `bundleCache` (unbounded `ConcurrentHashMap`). The `bundleCache` is keyed by `(Locale, baseName)` where the locale originates from the HTTP `Accept-Language` header. In applications that explicitly register a `ResourceBundleMessageSource` bean and serve HTML error responses, an unauthenticated attacker can exhaust heap memory by sending requests with large numbers of unique `Accept-Language` values, each causing a new entry in the unbounded `bundleCache`. Unlike GHSA-2hcp-gjrf-7fhc and the sibling `messageCache` (both bounded), `bundleCache` was not updated to use a bounded cache implementation.

## Details

The `bundleCache` is initialized in `inject/src/main/java/io/micronaut/context/i18n/ResourceBundleMessageSource.java` at line 150:

```java // ResourceBundleMessageSource.java:139-152 protected Map<MessageKey, Optional<String>> buildMessageCache() { return new ConcurrentLinkedHashMap.Builder<MessageKey, Optional<String>>() .maximumWeightedCapacity(100) // ← BOUNDED ✓ .build(); }

protected Map<MessageKey, Optional<ResourceBundle>> buildBundleCache() { return new ConcurrentHashMap<>(18); // ← UNBOUNDED ✗ } ```

The `resolveBundle()` method at line 169 inserts into `bundleCache` with no eviction policy:

```java // ResourceBundleMessageSource.java:169-185 private Optional<ResourceBundle> resolveBun…