High

Micronaut vulnerable to DoS via crafted form-urlencoded body binding with descending array indices

  • Disclosed: 17.03.2026
  • Updated: 11.10.2026 13:20

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

java
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).

Patches

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.

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

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Java / Kotlin (Maven) io.micronaut:micronaut-json-core >= 4.0.0-M1, < 4.10.16, >= 3.9.0, < 3.10.5, < 3.8.13 4.10.16, 3.10.5, 3.8.13

References

CVSS score -
CVSS vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Weakness (CWE)
CWE-835
Platform
Java / Kotlin (Maven)
Package
io.micronaut:micronaut-json-core
Disclosed
17.03.2026
Updated
11.10.2026 13:20

Sources and licenses

OSV / GitHub Advisory Database - GHSA-43w5-mmxv-cpvh - CC BY 4.0

Vulnerability history: io.micronaut:micronaut-json-core

All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.

This is the only known vulnerability of this package.

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