Summary
Micronaut vulnerable to DoS via crafted form-urlencoded body binding with descending array indices
In JsonBeanPropertyBinder::expandArrayToThreshold in io.micronaut:micronaut-json-core before Micronaut 4 4.10.16 and in Micronaut 3 before 3.10.5 does not correctly handle descending array index order during form-urlencoded body binding, which allows remote attackers to cause a denial of service (non-terminating loop, CPU exhaustion, and OutOfMemoryError) via crafted indexed form parameters (e.g., authors[1].name followed by authors[0].name).
Example
With such an application
package dosform;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.MediaType;
import io.micronaut.http.annotation.Body;
import io.micronaut.http.annotation.Consumes;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Post;
import io.micronaut.http.annotation.Produces;
import java.net.URI;
@Controller
class HomeController {
@Produces(MediaType.TEXT_HTML)
@Get
String index() {
return """
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<form action="/submit" method="post">
<label for="firstAuthor">Fist Author</label>
<input id="firstAuthor" name="authors[0].name" type="text"/>
<label for="secondAuthor">Second Author</label>
<input id="secondAuthor" name="authors[1].name" type="text"/>
<label for="thirdAuthor">Third Author</label>
<input id="thirdAuthor" name="authors[2].name" type="text"/>
<button type="submit">Submit</button>
</form>
</body>
</html>
""";
}
@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
@Post("/submit")
HttpResponse<?> submit(@Body Book book) {
return HttpResponse.seeOther(URI.create("/"));
}
}
package dosform;
import io.micronaut.core.annotation.Introspected;
import java.util.Objects;
@Introspected
public class Author {
private String name;
public String getName() { return name; }
public void setName(String name) { this.name = name; }
@Override
public final boolean equals(Object o) {
if (!(o instanceof Author)) return false;
Author author = (Author) o;
return Objects.equals(name, author.name);
}
@Override
public int hashCode() {
return Objects.hashCode(name);
}
@Override
public String toString() {
return "Author{" +
"name='" + name + '\'' +
'}';
}
}
package dosform;
import io.micronaut.core.annotation.Introspected;
import java.util.List;
import java.util.Objects;
@Introspected
public class Book {
private List<Author> authors;
public List<Author> getAuthors() { return authors; }
public void setAuthors(List<Author> authors) { this.authors = authors; }
@Override
public final boolean equals(Object o) {
if (!(o instanceof Book)) return false;
Book book = (Book) o;
return Objects.equals(authors, book.authors);
}
@Override
public int hashCode() {
return Objects.hashCode(authors);
}
@Override
public String toString() {
return "Book{" +
"authors=" + authors +
'}';
}
}
Sending curl -v -X POST 'http://127.0.0.1:8080/submit' -H 'Content-Type: application/x-www-form-urlencoded' --data-urlencode 'authors[1].name=RobertGalbraith' --data-urlencode 'authors[0].name=JKRowling' causes sustained CPU usage and unbounded memory growth (eventually OutOfMemoryError).
Workarounds
There is no way for users to fix or remediate the vulnerability without upgrading.
References
PR Fix: https://github.com/micronaut-projects/micronaut-core/pull/12410
Impact
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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See it in your environmentNew to Kodem? Get a demo →Remediation advice
For Micronaut 4, the problem has been patched in micronaut-core, dependencies with group id io.micronaut, since 4.10.16.
For Micronaut 3, the problem has been patched since 3.10.5
Users upgrade to the latest version of the framework.
Frequently Asked Questions
- What is CVE-2026-33013? CVE-2026-33013 is a high-severity security vulnerability in io.micronaut:micronaut-json-core (maven), affecting versions >= 4.0.0-M1, < 4.10.16. It is fixed in 4.10.16, 3.10.5, 3.8.13.
- Which versions of io.micronaut:micronaut-json-core are affected by CVE-2026-33013? io.micronaut:micronaut-json-core (maven) versions >= 4.0.0-M1, < 4.10.16 is affected.
- Is there a fix for CVE-2026-33013? Yes. CVE-2026-33013 is fixed in 4.10.16, 3.10.5, 3.8.13. Upgrade to this version or later.
- Is CVE-2026-33013 exploitable, and should I be worried? Whether CVE-2026-33013 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
- What actually determines whether CVE-2026-33013 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.
- How do I fix CVE-2026-33013?
- Upgrade
io.micronaut:micronaut-json-coreto 4.10.16 or later - Upgrade
io.micronaut:micronaut-json-coreto 3.10.5 or later - Upgrade
io.micronaut:micronaut-json-coreto 3.8.13 or later
- Upgrade