CVE-2026-44241 Micronaut has unbounded `formattersCache` in `TimeConverterRegistrar` that Allows Memory Exhaustion via `Accept-Language` Header
An unauthenticated attacker can exhaust JVM heap memory by sending requests with unique Accept-Language headers, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-44241?
CVE-2026-44241 is a high-severity denial of service vulnerability in micronaut-projects micronaut-core, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Micronaut Framework is a JVM-based full stack Java framework designed for building modular, easily testable JVM applications. From 4.3.0 to before 4.10.22, 3.10.6, and 3.8.14, TimeConverterRegistrar caches DateTimeFormatter instances in an unbounded ConcurrentHashMap<String, DateTimeFormatter> whose key is derived from the @Format annotation pattern concatenated with the locale from the HTTP Accept-Language header. Because Locale.forLanguageTag() accepts arbitrary BCP 47 private-use extensions (en-x-a001, en-x-a002, …), an unauthenticated attacker can generate an unlimited number of unique cache keys by sending requests with novel locale tags, growing the cache until heap memory is exhausted and the JVM crashes. This vulnerability is fixed in 4.10.22, 3.10.6, and 3.8.14.
Weakness: CWE-400
Which versions are affected by CVE-2026-44241?
6 open source packages ship an affected version, including io.micronaut:micronaut-context.
| Package | Affected | Fixed in |
|---|---|---|
io.micronaut:micronaut-context Maven | All versions | 3.8.14 |
io.micronaut:micronaut-context Maven | All versions | 3.8.14 |
io.micronaut:micronaut-context Maven | From 3.10.0 | 3.10.6 |
io.micronaut:micronaut-context Maven | From 3.10.0 | 3.10.6 |
io.micronaut:micronaut-context Maven | From 4.3.0 | 4.10.22 |
io.micronaut:micronaut-context Maven | From 4.3.0 | 4.10.22 |
How do I fix CVE-2026-44241?
Upgrade io.micronaut:micronaut-context to a fixed version for your release line: 3.8.14, 3.10.6 or 4.10.22.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-44241 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44241 exists.
Sources
Also known as CLEANSTART-2026-VZ67259, ECHO-7c8b-c5a6-558d, GHSA-8hjv-92q9-g4xj.